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WebObjects/Hands On: Hello World - Your First WebObjects Application

The contents of this wikibook are out of date and have now moved to http://wiki.objectstyle.org/confluence/display/WO/Home.

Create a New WebObjects Project
Launch Xcode (found in Developer->Applications). Choose ‘New Project...’ from the ‘File’ menu to display to ‘New Project’ Assistant. Scroll to the bottom of the list of project types and choose ‘WebObjects Application’.

Click ‘Next’. Type ‘HelloWorld’ as the ‘Project Name’ and click on the ‘Set...’ button to specify that you’d like to save your project to the desktop, or where ever you’d like to save your project. Note that earlier versions of WebObjects had problems building projects if their path had any spaces.

Click ‘Next’ lots more times until you come to a ‘Finish’ button, and click it (we’ll cover all those other screens later). If you did everything right, you’ll end up with something that looks like this (depending on how you’ve configured Xcode).

Edit the ‘Main’ Component
You should now be looking at a brand-new WebObjects project. This is your ‘blank canvas’ if you’re fond of analogies. It may seem a little complicated if you’re used to creating web sites that consist only of HTML files and images, but it isn’t too much more complicated. The main files we’re interested in are in the ‘Web Components’ group.

When you first create a WebObjects project, you will have just one ‘Component’, the ‘Main’ one. A WebObjects component consists of a folder and a bunch of files, but at this stage we’re really only interested in 2:  Main.wo - which contains the interface Main.java - where we’ll put the logic for the Main.wo page.  Double-click on the ‘Main.wo’ file to edit the interface in WebObjects Builder.

￼You should see something like the screen above. This is how a WebObjects component looks in WebObjects Builder. The top half of the window is a What-You-See-Is-What-You-Get (most of the time (WYSIWYG(MOTT)) HTML editor where you can design your pages. The bottom half of the window is used to connect interface elements to variables in the ‘logic’ section of your web application. Add the text “Hello, what is your name?” by typing in the top half of the window.

Add some form elements to the page by selecting a ‘WOForm’, a ‘Text Field’ and a ‘Submit Button’ from the ‘Forms’ menu bar item. Finally, add a place-holder String2 by selecting ‘String’ from the ‘WebObject’ menu bar item. You now have a finished interface: a heading inviting visitors to your web application to enter their name, a text field where they can type their name, a button so they can submit the form and a place-holder for the string of characters that you want to display in response.

Add an Action and a Key
Now that you have an interface, you need to write the logic of your first WebObjects application. This application allows a user to type their name in to a form and displays a message in response. In order to achieve this, we’re going to write a little Java code. Each WebObjects component has a Java file that contains the logic for the component. Java is an object-oriented programming language so if you’re not familiar with object-oriented programming the next section might introduce some new concepts. At this stage you don’t need to know the gory details of object-oriented programming, but it might help to understand some basic terminology. Each Java file contains a class which is like a recipe (it seems I like the analogies). The class contains both variables which are kind of like ingredients and methods which are like the steps in a recipe. The main difference between a Java class and a recipe is that with Java you don’t know what you’re baking until you start, so whilst a recipe might say ‘take 1 cup of flour and mix it’, a Java class will say ‘take 1 cup of stuff and mix it’ and you get to decide exactly what stuff is when the application is running. Anyway, enough background - let’s get our hands dirty. In order for our application to behave in the way that we want we need to modify the ‘Main’ class associated with our page. We want to add two things: a variable (think ingredient) to keep track of what the user types in and a method (think step) outlining what we should do with the variable. To make matters even more interesting, WebObjects builder uses its own terminology when talking about variables and methods. It refers to ‘Keys’ and ‘Actions’. I’m going to do what WebObjects should and make things simpler by using the terminology that the rest of the world uses to refer to Java classes, so when WebObjects says ‘Key’ think ‘Variable’ and when you hear ‘Action’ think ‘Method’ (you’ll get used to it).

So, to add a variable to keep track of our visitors name, click on the ‘Interface’ menu bar item and select ‘Add Key...’.

In the property sheet that slides down, type visitorsName (the capitalisation is a convention when programming in Java) in the ‘Name’ field, ‘String’ in the ‘Type’ field and make sure ‘An instance variable’ is ticked before clicking ‘Add’.

You should now see ‘visitorsName’ in the bottom-half of the window under ‘Application’ and ‘Session’. This indicates that the Java class associated with this component has a variable called visitorsName that is available to ‘bind’ to interface components. Repeat this step to add a ‘message’ variable to the ‘Main’ component. Next, we need to add a method to the class that we will execute when visitors click on the submit button. Click again on the ‘Interface’ menu item and this time choose ‘Add Action...’.

Type ‘sayHello’ as the ‘Action name’ and click ‘Add’. Open up the Main.java file to see the variables and method that have been added to this file. It should now look like the code below: public class Main extends WOComponent { public String visitorsName; public String message; public Main(WOContext context) { super(context); }

public WOComponent sayHello { return null; } }

Connect the Interface to the Logic
Now you’ve created the interface and added a variable and method to the underlying Java code, all that we need to do is ‘hook-up’ the interface to the logic. We need to specify that the ‘sayHello’ method should happen when the button is clicked and that the value for the ‘visitorsName’ variable should come from the text field. To do this we need to switch back to WebObjects Builder.

Click and drag from the space next to ‘visitorsName’ in the bottom half of the window to the text field and choose ‘value’ from the drop-down menu to indicate that you want the ‘visitorsName’ variable to get its value from the text field. Repeat this step to bind the ‘value’ of the dynamic String to the ‘message’ variable and the ‘action’ of the ‘Submit’ button to the ‘sayHello’ method in the underlying Java class.

Once you’ve hooked up the interface to the logic, the only thing left to do is write a line (or two) of Java code to compose a custom message in response to the click of the button.

Edit the Java Code
Open the ‘Main.java’ file by double-clicking on it. Fill out the details of the sayHello method like the example below. Basically, when this method is executed we want to construct a custom message based on the variable ‘visitorsName’ which will contain the name of the person we want to greet. public class Main extends WOComponent { public String visitorsName; public String message; public Main(WOContext context) { super(context); }

public WOComponent sayHello { message = "Hi there, " + visitorsName + "!"; return null; } }

Congratulations - you’ve just written your first WebObjects application. Make sure you’ve saved both the Main.wo file in WebObjects Builder and the Main.java file in XCode and you’re ready to compile your code and run the application. Click on the ‘Build and Go’ button in XCode to test your application.


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Movie Making Manual/Cinematography/Cameras and Formats/Human Visual System

=Human Visual System=

Yes, this article is a bit tongue-in-cheek! Of course it's not possible to produce a concrete list of "specifications" for the human visual system because it functions in such a fundamentally different way to a man-made-camera. Oh, and there's the small issue that we didn't design the eye. If we're being completely honest then we have to admit that our understanding of the human visual system is patchy. That said, it is useful and interesting to compare the human eye to man-made cameras. Not least because an important aim of photography and cinematography is to exploit and mimic the various eccentricities of the human visual system.

Dynamic Range
At any given instant, the retina can resolve a contrast ratio of around 100:1 (about 6 1/2 stops). As soon as your eye moves (saccades) it re-adjusts its exposure both chemically and by adjusting the iris. This is like having a camera on auto exposure. Hence, over time, you can resolve a contrast ratio of about 1,000,000:1 (about 20 stops).

The challenge for photographic systems is to display far more than the eye can instantaneously resolve, so that we can "read" a scene.

Typically a screen-projected image (film, DLP, whatever) won't ever have a brightness range of more than 1,000:1 and often less. If you make brighter highlights then scattered light from those areas of the screen will light up the shadows. This is where curve shaping (the S shape of film stocks etc) comes in to pack more original scene brightness in at each end of the range without apparently reducing the contrast of the mid-tones.

WikiPedia Articles

 * Human Eye

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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User:Enochlau

See w:User:Enochlau.

title: User:Enochlau


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A-level Physics/Forces, Fields and Energy/Gravitational fields

We have already met gravitational fields, where the gravitational field strength of a planet multiplied by an objects mass gives us the weight of that object, and that the gravitational field strength, $$g$$ of Earth is equal to the acceleration of free fall at its surface, $$9.81\, \mathrm{ms^{-2}}$$. We will now consider gravitational fields that are not uniform and how to calculate the value of $$g$$ for any given mass.

Gravity as a field of force
The effects of the Earth's gravity extend far out into space. For example, the Moon is kept in orbit by the Earth even though it is 400,000 km away (where gravity is the centripetal force). The Earth has a gravitational field that will attract any object with mass towards the centre of the planet.

Radial Fields

Gravitational field is a region surrounding the earth in which another object feels force of attraction. Direction of this force is towards centre of the earth, or the center of the mass in general. Further objects feel less force attraction whereas closer objects feel more force of attraction.

Uniform fields

A uniform field, however, has the lines perfectly parallel. The Earth's gravitational field can be considered to be uniform on the scale of small things such as cars, balls, and planes. For small heights at this scale (a few dozen kilometres), the strength of the field doesn't change enough to be noticeable. Again, the arrows point towards the centre of the Earth, since that is the way objects fall.

Newton's ideas of gravity
Isaac Newton was trying to find a way to explain why objects fell towards the centre of the Earth instead of simply staying put. He began to link the falling of an apple, with the "falling" of the Moon towards the Earth, and came up with his law of gravitation.

He suggested that any two objects with a mass would have a force of attraction between them. This force of attraction would be proportional to their masses, so that larger masses would have a stronger force of attraction than a smaller mass.

The gravitational field of every object is a radial field, since the mass is concentrated at the objects centre, and as you already know, this is the point at which gravity could be said to act.

The strength of a radial field decreases as you move further away from it. As you can see on the diagram on the right, the number of field lines going through the plane quarter when the distance is doubled, and it will be $$\frac {1}{9}$$ of the original value if the distance was tripled.

This is called the inverse square law, and is true for anything which is a point source, such a light from a point or the amount of radiation emitted.

The inverse square law follows $$\frac {1}{r^2}$$.

Using the above, Newton suggested that the force of attraction was proportional to the two masses as well as the distance between them:

 * $$F \propto \frac {m_1 m_2}{r^2}$$.

This relationship is the basis of how Newton's law of gravitation is often stated:

Any two point masses attract each other with a force that is proportional to each of their masses and inversely proportional to the square of the distance between them.

However, to make this into an equation, we need to add in a constant of proportionality, G:

 * $$F=-G\frac {m_1 m_2}{r^2}$$.

Where G is the gravitational constant, $$6.67 \times 10^{-11}\ \mathrm{N\cdot m^2 \cdot kg^{-2}}$$. There is also a minus sign in the equation, which will be explained in the "electric fields" module, where we will encounter repelling as well as attracting forces.

$$F=-G\frac {m_1 m_2}{r^2}$$ is also sometimes written as $$F=-G\frac {M m}{r^2}$$, so that capital M represents a large mass such a planet, and lower case m represents a small mass such as a ball or an aeroplane.

Defining the gravitational field strength
The gravitational field strength tells us how strong a gravitational field is. You may recall that the gravitational field strength of the Earth near its surface is $$9.81\,\mathrm{m/s^{2}}$$. This means an object that is near the surface of the earth will accelerate towards it at $$9.81\,\mathrm{m/s^{2}}$$. We could then define the gravitational field strength as the acceleration an object will experience within that gravitational field.

A better definition, however, can be derived from the equation, $$F=ma$$. Making $$a$$ the subject of this gives us $$a=\frac {F}{m}$$, or $$g=\frac {F}{m}$$. From this arrangement of the equation, our definition of gravitational field strength now becomes:

The gravitational field strength at a point is the gravitational force exerted per unit mass placed at that point.

This means that the gravitational field strength, $$g$$ is equal to the force experienced by a mass of 1 kg in that gravitational field.

From the new definition, it follows that gravitational field strength is measured in $$\mathrm {N\ kg^{-1}}$$, though it is perfectly acceptable to use $$\mathrm{ms^{-2}}$$ for situations where it is treated as an acceleration (such as the acceleration of an object in free fall).

Finding the field strength of a mass
Since $$F=-G \frac {M m}{r^2}$$ and $$\ F=mg$$, they can be combined to give:

 * $$mg=-G \frac {M m}{r^2}$$ (by substituting F for mg)

 * $$g=-G \frac {M}{r^2}$$ (by cancelling the lower case 'm's)

You can use this to find the gravitational field strength of a mass at a particular point, r.

Note that the gravitational field strength of the Earth near its surface is numerically equal to the acceleration of free fall, $$9.81\ \mathrm{m s^{-2}}$$.


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User talk:RobinH

Publishing Wikibooks
Yes, getting a PDF file is indeed the very next that needs to happen, and I'm glad that you are working on that. What comes after that is going to require a bit of money, and we as a group of Wikibooks editors need to decide if we are going to stick with the Wikimedia Foundation (or work under it), or perhaps go off and start our own little group for the things that are going to require some money. I would prefer this secondary approach, of trying to establish a non-profit organization that is organized to physically publish content from Wikibooks. I've approached several other people here on Wikibooks that are interested, but for now I've kept this idea rather low-key.

What I'd like to do is to register a ISBN publisher code for Wikibooks that would be owned by this publishing group, and to set up some sort of e-commerce website to offer direct sales of Wikibooks content. Political and financial control of the group would be organized along the lines of a commercial cooperative with an exact heirarchy and format that we can decide once we have some content to work with. As for the physical publishing of the content, I already have some experience with that, including one Wikibook that is sitting right in front of me that is dog-eared from my kids going through it. (I physically published the Wikijunior Solar System book for a few people near where I live.)

All of this both requires some money, but it also has a small revenue stream as well. I want to get this very well organized, and I also want to be very careful because I don't want Wikibooks to turn into a vanity press either. It certainly has the potential of becoming that if we don't watch out. I believe that once we have some outstanding content, given our relationship to Wikipedia and general visibility that Wikibooks already has, book distributors are going to come to us asking to use our content. Or just out right stealing it and publishing it themselves. Either way I don't mind, but this at least allows us to get something going and can get this content to other places that would not normally be reading something from Wikibooks. --Rob Horning 19:55, 25 January 2006 (UTC)

 * Certainly Wikibooks is an excellent "route to market" - even if, as in this case, the online product is substantially free.

 * I would be interested in your draft corporate constitution. Monitoring the accounts would be most problematical if the people contributing money are in disparate parts of the world -do you think that official reports of the Pay Pal account, or account of whatever system is being used, would need to be accessible to the senior project team? I know this sounds very 1980s but I believe that the principle people involved should be allowed to have an adequate reward, such as a percentage of profits, as a motivation for producing and marketing hard copy.

 * Quality, consistency and completeness are the main problems with the adult texts. It is also amazing to me that the high school texts are so incomplete. The lack of quality chemistry, physics, biology, maths, US history, general history, world geography, english and french textbooks at the high school level is very surprising. Perhaps three or four contributors could focus on each of these in turn. RobinH 09:28, 26 January 2006 (UTC)

Have you considered A Print on demand publisher. They pay quite high roylaties(20 - 30%), which could help defray any costs, or be returned, in whole or part to wikibooks or the wikimedia foundation, or given to another charity. gets it in print fairly cheaply, without much rick of over printing, and keeps it in print for as long as neccesary. Normally requires copyright to be owned by the person submitting it ot thwem, but if you explain the copyright situation with wikibooks, they would probaly be ok with that. Arima looks good. I am not affiliated with them in any way, just for the record. Arima Dolive35 11:29, 17 May 2006 (UTC)

Two things
Have you seen Talk:Consciousness studies? There are some lost pages that may be useful for the book.

Besides, have you seen Help:Print versions? It is possible to create an automatically updated page with all book contents, which can also be used to create a PDF version. I can help you if you are interested in such solution. --Derbeth talk 18:30, 8 February 2006 (UTC)

 * Consciousness studies :Other explanations
 * This page was created in error by a new user of Wikimedia and its content is now at: http://en.wikibooks.org/wiki/Consciousness_studies:_BioPsychoSociology and can be deleted.

 * Consciousness studies:The philosophical problem - Appendixr
 * This page has been integrated into http://en.wikibooks.org/wiki/Consciousness_studies:The_philosophical_problem_-_machine_consciousness#Elementary_Information_and_Information_Systems_Theory and was used as a place holder for a while, it can also be deleted.

On the subject of a print version, I will have a go at this in the next week or so if you like. The conversion from the print version to PDF is a bit of a mystery for me! Best Wishes RobinH 11:32, 9 February 2006 (UTC)

 * What the heck. Work is boring so I have just done a preliminary print version at:

http://en.wikibooks.org/wiki/Consciousness_studies/Print_version

RobinH 12:32, 9 February 2006 (UTC)

Maximum size of PDF files?
Your PDF works just fine for me and looks great. I suppose you met some server problems. BTW, I added link to Print version page to Consciousness studies main page. --Derbeth talk 11:57, 16 February 2006 (UTC)

 * How did you create this PDF? --Derbeth talk 11:58, 16 February 2006 (UTC)

 * I made the print version then viewed and saved it. I opened this file in MS Word and saved it once more in Word format. This allowed Word to set the pagination, produce a TOC etc. The document "read" differently as a whole book so I did some final edits and juggled with the image placements. I then downloaded PDFCreator and printed the Word document to PDF.  This preserved the page breaks, which are the big problem with the HTML original whether printed direct or converted to PDF and printed.

 * I tried to upload the PDF in Wikibooks but, although it would upload it could not be viewed. At the moment the PDF is being hosted on another site ( http://www.users.globalnet.co.uk/~lka/Consciousness%20studies.pdf ).

 * This is the file that is uploaded to Wikibooks:

 * http://upload.wikimedia.org/wikibooks/en/b/bb/Consciousness_studies.pdf

 * Is the PDF at Wikibooks the same as the first one? It works fine. --Derbeth talk 14:04, 16 February 2006 (UTC)

 * The PDFs are the same. When I click on the link http://upload.wikimedia.org/wikibooks/en/b/bb/Consciousness_studies.pdf I get a white explorer screen for about 15 minutes then a message to the effect that adobe has "timed out" (I am using a 1 meg broadband connection - the link http://www.users.globalnet.co.uk/~lka/Consciousness%20studies.pdf takes about 20 secs to download and view). If I upload a PDF file of about 300kb to Wikibooks I can view this almost immediately, which is why I asked if there was a size limitation (The full file is about 1.8 Mb). RobinH 15:37, 16 February 2006 (UTC)

 * PDF from Wikibooks works in my Opera, I also checked it in Firefox - loading it took 2 minutes, but I also download other things. Ask someone else if everything is ok, in my opinion your problems were just an accident. --Derbeth talk 18:56, 16 February 2006 (UTC)

 * Well, if you can get http://upload.wikimedia.org/wikibooks/en/b/bb/Consciousness_studies.pdf

the problem seems like it should be at my end. I removed my firewall but still had a no joy... RobinH 19:39, 16 February 2006 (UTC)

 * The PDF file looks fine to me as well (at least for being able to download the content). Actually, I am very impressed with the overall appearance of the book itself.  I'm using Mozilla, and generally I download the PDF files directly to my hard drive, because they tend to lock up my browser with the plug-in support.  I would like to add that you should consider adding the names of some of the major contributors to the content (the GFDL requires the top 3-5 authors... U.S. copyright law requires all of them (except obvious vandals who have been reverted).  You also need to include the GFDL within the contents of the book, even though it can be very fine print.  Otherwise, it is looking great!  --Rob Horning 00:20, 17 February 2006 (UTC)

 * Thanks for the suggestions, I have implemented these and re-uploaded.
 * I can right click on the Wikibooks URL for the PDF and save it without any problems. The difficulty arises when I left-click on it to open the PDF in Acrobat directly. From what you and Derbeth are saying it is likely to be some problem at my end. However, I can link directly to PDFs everywhere else so, just in case anyone else has my problem, I have included instructions on how to save the file to disk - which is probably a good idea with a 225 page book anyway. RobinH 19:47, 17 February 2006 (UTC)

Test layout for well developed books

 * The problem with these Wikibooks is that according to our copyrights 5 main authors of a book should be listed. The good practise is to create special page "Authors" listing most important contributors; it can be included to print version just as another chapters. I suggest that you create such pages for these books if they don't have them. --Derbeth talk 11:27, 25 February 2006 (UTC)

Linking to PDF
Please do not link to PDF's using direct URL. Such PDF's are shown in unused file list. Use Media: link instead. --Derbeth talk 13:39, 8 March 2006 (UTC)

 * Thanks. I'll have to do a bit of cleaning up.... RobinH 14:11, 8 March 2006 (UTC)

Previous PDF Editions
See my talk page on how to change it. The reason was you used the wrong syntax. Help:Print versions warns not to link to PDF's like:, because it causes entire PDF to be loaded with page. You should use Image:.... Please fix it if you used this syntax. --Derbeth talk 19:45, 9 March 2006 (UTC)

Hot Picks
RobinH, you are a storehouse of great information of which books are the most advanced and ready for PDFs, and I'd like your help with the list of Hot Picks for the Main Page. I saw somewhere you said that you have a list of 25-30 good books that you found here on the site. Could you hook me up with a list of those, pleeeease? Thank you! --Karl Wick 23:27, 9 March 2006 (UTC)

 * Thank you very much RobinH, your work has introduced me to several great books that I would not have known about otherwise! --Karl Wick 21:33, 10 March 2006 (UTC)

Please help with “Special Relativity: Spacetime”
Hi Robin! Thanks for your awesome work on the Special Relativity wikibook. I’ve been meaning to try to grok the basics of relativity, and now that there is a cool wikibook I have a good excuse (I can pretend I’m proofreading or something).

Anyway, please take a look at Talk:Special Relativity: Spacetime. It’s just a minor issue, but I’m really not good at this relativity business. — Daniel Brockman 10:52, 29 March 2006 (UTC)

Hi! I was just poking around after initializing an WikiBooks account. I saw your notice (8 April) in the staff lounge about moving this discussion to ... something. Might I suggest that would best be a link to allow continuity.
 * I'm curious to see for such proposals you WikiBookians aren't using an RFC WB:RFC project page to discuss guidelines and policy proposals as I understand to be historic wiki tradition (i.e. pre-wikipedia foundation). Obviously, I'm a total newbie here, but such forums categorize and focus the discussion to the topic at hand, leaving the lounge uncluttered save for mentions of the original and the links to same. Fra nkB 17:17, 8 April 2006 (UTC)
 * 'scuse me for the mess... I'm having trouble getting my signature to work correctly here. It's supposed to look like the above hand encoded one, so there are some Meta or implimentation differences!

Fabartus//[[User talk:Fabartus]] 17:45, 8 April 2006 (UTC)
 * Hi again.
 * I never got to my WikiWork today as I browsed through the staff lounge and saw a familiar theme from various wikipedia archives, this time, in time to make a timely contribution. I've also taken a good read on special relativity, and so kudos!Fabartus//[[User talk:Fabartus]] 21:00, 8 April 2006 (UTC) (I wish I knew how to fix this sig!)

explain comment
My comment to jguk is only stating that as long as there is a question as to whether or not my effort on THINKSTARSHIP isin contravention, it seems irrational for me to continue that effort, until the issue of whether or not i am in contravention is resolved. It is not a personal attack, only stating that i'd like to see the issue resolved, and explaining that it makes no sense for me to continue working until it is. Prometheuspan 17:50, 26 April 2006 (UTC)

 * RobinH, let me assure you that I am not seeking to override a vote (although, following Robert Horning's comments in the Staff Lounge, I would question how you have determined what the result to be). What I do believe we should be looking for is consensus. There have been a number of comments made on the talk page of WB:NPA that should, in my opinion, be followed up. They are legitimate concerns (even if you disagree withthem), and surely you are not saying that the wording of WB:NPA is so perfect that it cannot be improved upon? There's no real need to rush things, it's clear that no-one is advocating making personal attacks on fellow wikibookians. I should therefore be grateful if you would do me the courtesy of responding to my concerns on WB:NPA, then letting a time pass for others to make comments if they seek fit, before seeking a vote under clear rules and time constraints, and with full publicity (along the lines Rob suggested) before marking the policy as "enforced". I'd also note that at worst (from your point of view) there should only be a two month delay in marking it as "enforced". Kind regards, Jguk 20:54, 26 April 2006 (UTC)

Since you left word on April 28th
Hi! RobinH—Sorry, I've been swamped over at Wikipedia and Life too! I'll take a peek at the policy proposals sometime this weekend. It's been a while so I don't know what good it will do! Best regards, FrankB-[[User talk:Fabartus]] 06:00, 6 May 2006 (UTC)

 * RobinH, I just read your message from April 28. It looks like your most desired policy, the Ad hoc administration committee, was not approved. Is there anything I can still do for you on this issue? I support the no personal attacks policy and the editing disputes policy. --Karl Wick 00:58, 22 May 2006 (UTC)

IRC
Robin, I know we have differences in methodology, but I really do think we are close in what we believe our aim should be. If you are able to come to irc on the #wikibooks channel, it would be good to talk through where and why we disagree, which would help us come to a solution which ought to be good for wikibooks as a whole, Jguk 18:22, 18 May 2006 (UTC)

Sorry, Micheal Robin John Jr., I am wasting Robin’s time and reacting money with nitrogen oxide. IRC is an good network services. Our aim is there. By copyright needed, 2001:56A:774D:8F00:F43C:B4DA:3B0B:94FC (discuss) 14:15, 9 June 2019 (UTC)

Behaviour policies
Why not rename No personal attacks so that it becomes Behaviour policy? By all means have a note on it saying that whilst the bits included are enforced, the policy is still undergoing development. Then propose adding bits, such as the editing disputes bit, to then-existing Behaviour policy.

Such an approach would: (1) Meet the requests of those who only want to see one behaviour policy; (2) Make policy easier to find because all related policy would be on one page; (3) Helps make sure that we do not make inconsistent policy (ie say something on one page and something else on another); (4) Helps us identify common themes which would allow some condensing of policy. As it is, the "editing disputes" and "no personal attacks" proposals have some overlap - for instance, certainly on Wikipedia, many editing disputes turn into personal attack wars and vice versa. It makes sense to consider these issues together, Jguk 16:12, 31 May 2006 (UTC)

 * This is an interesting idea that might be incorporated into your policy rewrite. The reason that I am keen to get the two behaviour policies into "enforced" status fairly soon is that I really do feel exposed at Wikibooks. I am contemplating writing a section on genetics in the GCSE Biology book and can just imagine some Intelligent Design/Creationist objector wrecking it. With the two policies in place we would have to discuss the problems outside of the book, we would be forced to be civilised and finally, if agreement were not possible, an administrator could be asked to adjudicate. This might result in an ID appendix or similar (hopefully not) but would not wreck the book. RobinH 16:37, 31 May 2006 (UTC)

The GCSE Biology book needs to have content relevant to the GCSE syllabus (which one is being applied should be identified), and nothing that is irrelevant to the syllabus. I'm aware that one board is now proposing to teach (at least a little bit of) creationism - and therefore it should be covered to such an extent as is required to meet with that syllabus's requirements - no more, no less. Similarly, whatever you write on genetics should be based solely on the syllabus requirements, and you should not let any personal views you may have on the subject affect what you write. If anyone tries to remove (as opposed to rephrase) material that is relevant to the syllabus, or add information that is unrelated to the syllabus, then let me assure you of my support in stopping them. I believe this is justified under current (unwritten) policy.

Incidentally, your "editing disputes" proposal would not help you here. It would give the person disrupting you the upper hand (as you would be the one to do the first "revert", you would have to give way or fall foul of the proposed three revert rule. You also wouldn't be able to re-address the issue ever again without risking being banned.

 * Unlike the Wikipedia three revert rule we would need to show evidence of an attempt at compromise on a disputed edit page. If compromise were not possible an admin would need to be involved and the matter could be pushed to a vote. RobinH 18:11, 31 May 2006 (UTC)

It's for reasons such as this that I do not like prescriptive rules that address only some potential issues. I appreciate that your proposals are well-intentioned, I just think they unintentionally open up a hornet's nest too. Non-prescriptive principle-based rules are far more flexible in that regard - for example, in the situation you outline someone can come in, see that you are trying to have a book that reflects the syllabus and another person is disrupting you rather than helping you, and come down hard on the one being disruptive without having to sanction you. All the best, Jguk 16:57, 31 May 2006 (UTC)

 * The problem with a non-prescriptive basis is that it puts all of the power in the hands of admins. We have already seen wheel wars at Wikibooks... RobinH 18:11, 31 May 2006 (UTC)

 * Incidentally, where are the wheel wars? I've seen others mention this, but I don't think I've seen it on Wikibooks, Jguk 18:41, 31 May 2006 (UTC)

GCSE Biology
You refer to the GCSE Biology book above, but we don't have one, do we? If you're about to start one, that would be great - and maybe Wikipedia's Biology WikiProject could help. Have you seen Wikistudy? It would fit in well there, Jguk 17:03, 31 May 2006 (UTC)

 * See GCSE Science/Contents. I have 2 sons who have done this course and who have bookshelves full of textbooks and revision guides. I also have a PhD in biophysics. RobinH 18:05, 31 May 2006 (UTC)

Great stuff! I'd love to see Wikibooks host books for all core GCSE and A-level syllabuses - which is one of the reasons I put the Wikistudy idea forward. There appears to be a lot of goodwill for such a project, but it just has not been harnessed together in one place yet. Hopefully it will happen, and hopefully it will happen here at Wikibooks, Jguk 18:42, 31 May 2006 (UTC)

Game Guides
Wow, nice to see someone fighting so much for them :-) I am also a big fan, I much prefer my kids playing videogames than being TV couch potatos! I gave up on games at Wikibooks, but if you still want to  fight the battle here are some links for ya:
 * Interactive Arts and Media Course Diagrams Columbia College Chicago
 * Video Game Design Schools & Colleges (Check Devry's they are excellent!)
 * Video Game Design and Development at Northwestern

 * Robin, I'm not quite sure what point you are trying to make over at the staff lounge. It is accepted that there can be textbooks on games. However, games walkthroughs are not textbooks and should go. Jimbo's position has been quite clear on this from his amendment to WB:WIW (see ) onwards. I think you will find that Jimbo's mind is quite made up on this one, and will not change regardless of what arguments you or others put forward.

 * On a completely different note, it is clear that you care about Wikibooks, and I for one look forward to your future additions relating to GCSE Biology. May I ask whether you're willing to put yourself forward on WB:RFA? If you do, you can be sure of my support, Jguk 18:38, 1 June 2006 (UTC)

Policy Votes
I know you are working really hard to get all the policy here in order, and I certainly appreciate the effort. I feel that we as a community definately need these policies to operate better. However, the dispute resolution policy was too hard-edged as you put it, so I had to take my vote away. If you change it to milder language, I will probably put my vote back. --Whiteknight (talk) (projects) 23:23, 5 June 2006 (UTC)

I have to agree with Whiteknight. At this point, I think it would impede the work of the administrators, all of which I trust. Maybe if there were more contributors, or more problems with this type of thing, this would have an easier time getting passed. The last dispute I saw was with Jguk and Johnny, Jguk and Whiteknight seemed to handle the situation just fine, without this policy. DettoAltrimenti 00:40, 6 June 2006 (UTC)

 * Perhaps I should just tidy up the current loose ends in the area of policy and let the rest soak for a while. As you say, there is little real trouble at the moment. RobinH 08:28, 6 June 2006 (UTC)

Compliments
We're arguing over the Disputed Editing policy, and that's not so good, but I wanted you to know that I took a look at some of your pages on Turgor in plant cells and the structure of the eye, and found them to be useful and engaging. I wish I understood biology better than I do, and maybe this summer I'll run through the Wikibooks biology book and learn a few things. Thank you for working on that. -Andrew Watt 19:48, 6 June 2006 (UTC)

Creating PDF versions
Can you explain me, step by step, how do you create PDF files from print versions? I tried method described in Help:Print versions but it did not work. I was saving true print version (without navigation bar, print version notice and so on) as HTML file with images using Opera, Firefox and Internet Explorer and opening them as HTML file in OpenOffice.org 2.0.2 and Microsoft Word 2003. None of these combinations worked. The thing I got in word processor was text with print version notice, section edit links and so on. --Derbeth talk 14:03, 24 June 2006 (UTC)

 * I save articles as "Web page complete". MS Word displays the files properly for me (looking like the Print Version) provided they are small (under 50 pages). Larger files may need breaking into parts for viewing. Recently I have used Wordpad to "top and tail" the files before viewing. I remove all the unnecessary code before the BODY tag and after the end of text, before the /BODY tag. I just stick the standard HTML HEAD /HEAD sequence in front of the BODY tag.

 * Once the file has been saved as a word processor file it looks like the Print Version but does have irritating additions such as section templates still in place. I chop off the Print Version heading and any Table of Contents and use recorded macros in Word to cut out all the repeating elements that are not needed such as "edit" links and templates. I then page through the whole file looking for headings that have the wrong 'level', links that are incorrect and missing graphics. If there is a missing graphic I go to the online version and copy and paste the graphic into place. Once the text looks OK I insert a Cover Page and Table of Contents at the start. The whole process takes about 45 minutes for a 200 page book so it is a labour of love if you are a busy person. Once the Word Document is complete I print it to file using PDF Creator and upload.

 * Some books make Word 'hang' when you try to view them as HTML. The only way round this (that I have found) is to chop them into pieces, top and tail the small files with HTML tags and combine them in Word. RobinH 09:18, 26 June 2006 (UTC)

General voting rules/Proposal
Since I know you are very active in policy matters, I figured I would alert you, and get your opinion. I've created this proposal in response to some of the criticisms from the original proposal. This version removes all mention of percentages (which was a big stumbling block for some people), reinforces the notion of concensus, and generally tries to be more forgiving and friendly. I don't think this should go up for a vote the way it is, but I would like to get some other eyes on it, to fix any holes that i might have missed. --Whiteknight (talk) (projects) 17:13, 12 July 2006 (UTC)

 * I would like to call a vote on this new policy proposal by the end of the week sometime, and I wanted to know if you had any last minute comments or suggestions on it? If we can get an official voting policy on the books (even if it is vague and interpretable), we can start to move forward on some of the other policy proposals that have sat undecided for long periods of time. --Whiteknight (talk) (projects) 18:51, 31 July 2006 (UTC)

I changed some of your previous edits on this proposal, I hope you don't take offense to this. I am pushing for a more "freeform" version of this policy, with few strict guidelines, and plenty of room for interpretation. Setting specific timeframes, majority overrides, numbers of voting attempts, etc. seems counter-productive towards this end. My sincere hope is that the notions of "community" and "consensus" and "compromise" are put forward, and that people learn to work together towards a common goal. I know you are strongly concerned about the rights of the minority, so my rewrite here specifically mentions that minority opinions must be addressed before a final declaration of consensus. Users who are in stubborn, uncompromising opposition to a discussion, can be viewed as acting in bad faith, and not working towards compromise nor concensus. To this end, no single user nor a small minority can "block" a vote, but they can offer compromises which must be considered. Now, if it is found that minority opinions are stalemating some discussions, perhaps we can work out an alternate method of decision-making, such as 3rd-party arbitrators, subcommittees, etc. --Whiteknight (talk) (projects) 15:28, 7 August 2006 (UTC)

Modern Physics
Modern Physics is an epic project, which is why it saddens me to see it with so few reoccuring contributors. Most of the people who were a driving force for this book originally have not contributed in a year or more, and the book has essentially be left abandoned. I do agree however, that the material in Modern Physics is disparent enough to warrant being separated out into separate books, just as Special Relativity has been already. Perhaps I will work on separating out the material into new books, instead of trying to rename and reformat all of the current pages. The Gravity section, and the Constants appendix however, should probably remain in this book, because they are not big enough to be weaned from the mother quite yet. --Whiteknight (talk) (projects) 14:52, 17 July 2006 (UTC)

Hi Again
I've ported two new useful interwiki templates w2 & w2c from that allows pipetricks and interlanguage reaches to wikipedia pages & commons pages respectively (as demonstrated below)... depending on the users default language.

I'm very much involved in sisterwiki project cross linking studies and experiments (nothing yet seems absolutely workable), so if you'd be so kind as to drop your key template categories, I'll drop by later tonight and fix things up. The redlinks on that template obviously don't fit up well with what you're all using!

 * Also, take a look at &  and let me know if you want that big multiligual template on your main category page (this page) interestingly 'different' by name. // Fra nkB 20:36, 25 July 2006 (UTC)

 * Thank you for this information. Rob Horning, Whiteknight, Derbeth, Jguk and other active admins are probably better able to put this scheme into effect. RobinH 09:05, 26 July 2006 (UTC)

Human physiology textbook input request
Robin,

I saw that you are a retired physiologist. I am not a physiologist, but I am teaching introductory human physiology. Currently I am teaching the class to a remote site 90 miles away, and we decided to make a Wikibook instead of holding a traditional course. We have completed our first of three phases for our human physiology book, and I am quite proud of what the students have accomplished so far. Since you are very experienced with both physiology and Wikibooks, I wondered if you could look at our book and give us suggestions for where to go next. Whiteknight has helped us a lot with formatting questions. I would love to hear any thoughts from you on content, format, further directions, etc. Thanks! Provophys 14:39, 10 August 2006 (UTC)

General voting rules: note to admins
I mentioned on the voting rules that I would be sending out a note to all active admins, requesting that they come in and take a look at the current policy. Here is the text of the note that I will be copy+pasting on to each of their pages, and possibly staff lounge. I will wait for confirmation from you to make sure that it is fair, but descriptive:
 * I would like to personally call all active wikibooks admins and users to come take a look at the proposed version of the General Voting Rules policy that is currently under discussion. The current text of the policy puts a focus on "consensus" as the primary method of making decisions. However, it has been asserted that such a policy would allow disruptive or stubborn users to "block" votes, or prolong them indefinately. This policy has the power to affect all users here at wikibooks, and it is imperative therefore that all users read the proposed text of the policy, and join in the discussion.

Let me know if you like it. --Whiteknight (talk) (projects) 18:07, 10 August 2006 (UTC)

 * If we changed some text in the policy, to make it more like the original version, would the policy make more sense? I'm by no means in stubborn defense of this particular wording, I just want to address a few key points about "consensus", "compromise" and "community". I'd be willing to alter nearly all the text of this proposal, so long as we don't explicitly introduce a mechanism for majority voting (unless we include a clause that the method by which a decision is arrived at can be decided before the vote, so long as all participants agree on the terms). If we had enough ambiguity in the policy, so that consensus was the stated primary method of decision making, but other methods were implicitly allowed (assuming all members could agree on those other methods beforehand), I would be in favor of that policy as well. I do think that in some matters, wikibookians should be able to say "Okay, we have a disagreement on issue X, if everybody is okay with it, I would like to call a vote, and a 75% majority wins the day", especially in matters that are trivial (and I say trivial to mean local matters, such as issues concerning a single book, issues not affecting policy, etc). I don't think that such "alternate methods" should be allowed when discussin policy, VFD, RFA, or things of that nature, however. Let me know what you think beforehand, we could make some changes before we invite everybody in to look at it. --Whiteknight (talk) (projects) 13:48, 11 August 2006 (UTC)

Kellen's Version
I agree with you, I like the points of Kellen's version of this policy. However, I do think that for this policy proposal to "fit in" with the rest of our policy cannon, it should contain more prose, and fewer bullets. I'm going to be bold, and write up a prose version that mirrors the points from kellen's proposal. Hopefully, my rhetoric doesn't murk it up. --Whiteknight (talk) (projects) 19:38, 11 August 2006 (UTC)

WB:RFA
It must seem like I am polluting your talkspace, with all the messages I leave you. I promise I will stop for a while after this one. I just wanted to let you know that I've nominated you to become an admin here. We definately dont always agree on things, but I hardly think that is a requirement. I hope you accept your nomination. --Whiteknight (talk) (projects) 20:59, 11 August 2006 (UTC)

 * Thank you for proposing me as an admin. I am going on holiday for the next 2 weeks as of tomorrow (if we make it past the airport). I feel I should really be concentrating on books, especially GCSE Biology and sections on "Symmetry and Physical Laws" and Waves in the SR book. It would probably be best to leave adminship until I have got these books finished! RobinH 14:39, 14 August 2006 (UTC)

 * That's disapointing, but I understand the sentiment. I am highly convinced that you would make an excellent admin, so if you ever change your mind, you will have my vote. Have fun on holiday! --Whiteknight (talk) (projects) 14:42, 14 August 2006 (UTC)

Untagged Images
Hey robin, long time no see! I just wanted to let you know that within the next month or so, we are trying to delete all the untagged images on wikibooks (some of them are years old, and there are now more then 3000 of them). The records show that you have uploaded at least 7 images without licenses. you can see the list here. Since we all know you and trust you, If you tell me what license to release these images under, I will gladly tag them for you.

PS. I noticed that you don't have a valid email address stored in the system, and so I couldn't email you about this. I hope you see this message before images start getting deleted. --Whiteknight (talk) (projects) 14:02, 6 November 2006 (UTC)

 * Hi there! I have tagged these now. RobinH 16:06, 6 November 2006 (UTC)

Special Relativity
Hi RobinH,

thanks for the update/explanation about the SR Introduction. I understand that you agree and disagree with me on some points. That's fine. i think i may pull out of wikibooks special relativity because I feel I'm out of your league. The target audience may be closer to your demographic than the layperson-type that I thought it was aimed at. Perhaps in this case your appraoch is better suited for the intended audience. cheers!--Read-write-services 00:57, 20 November 2006 (UTC)

Ad in staff lounge
Hi Robin - thanks for dealing with it - I've put a block on the IP which may discourage further activity - regards -- Herby talk thyme 11:52, 16 December 2006 (UTC)

Wikibooks Newsletter, Volume 1
(Wikibooks gazette home | Discuss | Bulletin board | Subscription list)

This is a short newsletter that is being distributed to all active wikibookians. You are getting this message because you are recognized as an established contributor to the project. This newsletter will be distributed on a regular basis to help share news, information, and tips. It comes from a bot account, User:The Staff. User:The Staff is currently operated by a team of wikibooks admins, the complete list of which is available on the user page of the bot. If you would like to not receive this newletter anymore, please remove your name from the list at Active wikibookians.

The work you do at Wikibooks is greatly appreciated. However there are plenty of other opportunities for you to get involved and help us to create a thriving Wikibooks community. We are sure that there are things we can do to help you and your understanding of Wikibooks and similarly there are certainly things you could do to help Wikibooks become a better place.

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Sometimes it is easy to forget that the Wikibooks community is much larger and more diverse then the people who work in a single book, or on a single bookshelf. Hopefully, together we can all make Wikibooks a better place, and a more valuable educational resource.

The staff at Wikibooks 13:17, 21 December 2006 (UTC)

Active
Hi Robin - you are already in there!! The Gazette wouldn't have got to you otherwise - I'll revert - regards -- Herby talk thyme 17:43, 22 December 2006 (UTC)
 * OK  -- Herby talk thyme 17:44, 22 December 2006 (UTC)

Forking proposal
I noticed you had taken part in the policy discussion about forking, and wonder if you might weigh in at Forking proposal, which is about the technical side of making good forks. -- SB_Johnny | talk 13:35, 15 January 2007 (UTC)

I don't agree with your last edit of Wikibooks:What_is_Wikibooks/Unstable
Please think about using the content you added as a contribution into the Deletion policy or propose some sort of protection to those pages or redefine the content you are referring to as a proper and non subjective description and add to another place on the What is Wikibooks proposal, it doesn't make any sense stating a restriction without real limits on the Enforcement part of the policy. (I agree with such limitations, at least as much as I think I understand it) --Panic 20:34, 23 January 2007 (UTC)

 * User:Whiteknight [rewording] solves partially the problem but it is a duplication of what is already stated in the Deletion policy or at least in the unstable branch, I would prefer something like...

 * If any pages or books are added that are outside the scope of Wikibooks, they should be processed as described in the Deletion policy

 * ...and check that it the pages get some kind of protection there.--Panic 00:37, 24 January 2007 (UTC)

Wikibooks as content for printed textbooks in developing nations
I've searched around a bit for folks that are publishing Wikibooks at rockbottom costs (which means more volume than on-demand) for the purposes of providing textbooks in developing nations. I've gotten a couple of data points that show that crumby knock-off photo-copy versions of textbooks cost between $6 and $8 in Togo. (See, for example: http://far-togo.blogspot.com/2007/01/peace-corps-update-16.html .)  Separately, I've found that offset printing costs for moderately large volumes (10,000 and up) are below $2. A check of the pulp novel section of the local bookstore shows that really high volume printing costs must be under $1.

I mention all this because of my interest in lowering the barriers to education in poor nations. If the content is free (other pages around Wikibooks suggest that this can be achieved for printing purposes, if careful about fair use images), and the printing cost minimized, and distribution is handled by some charitable org, then one obstacle can be significantly reduced or even eliminated. I am interesting in supporting existing efforts, or if I don't find any, I'll look into starting an effort of my own.

I'm writing here because Google sent me here :-). I'm hopeful that you can direct me, or other readers can direct me. Thanks! (Readers, I can be reached at: curtbeckmann at gmail dot com) (Robin, if I have violated a protocol with this note, please let me know.)  --Curtbeckmann 23:56, 12 February 2007 (UTC)

 * Hi, and welcome to Wikibooks. Your best contact for low cost printing on Wikibooks is probably Rob Horning (See  Publishing etc).  Paperback prices are now surprisingly low, my company gets a 150 page manual with glossy cover printed for about £2.50 ($5) from a local printer if volumes are over 1000 copies.  It looks like a proper paperback, possibly better quality than most.  Have you thought of talking to a local printer and persuading him to do charitable printing for cost price?  I would guess that the cost price on our manuals is nearer $3 than $5.  You would need to supply the text "print ready" in Word or one of the Mac formats. (I bet you could get an even better deal in Hong Kong or New Delhi). RobinH 15:07, 13 February 2007 (UTC)
 * Thanks, Robin, I'll check into it. It would be cool to do the printing locally to the recipients, which may mean Africa; New Delhi may be good also.  Prices might not be the absolute lowest, but reducing shipping costs is worth something, plus driving production in the region is a worthy goal.  Thanks again.  --24.6.122.219 06:51, 14 February 2007 (UTC)

Re:Ad Hoc Arbitration
What I was talking about with my comment against Ad hoc arbitration is the ability of a person to act as an arbiter and impose a binding solution without a proper arbitration policy to back it up. There are some people here who are more qualified to impose solutions onto disputes then other people are. This is a function of experience and knowledge of wikibooks policy.

Arbitration is very serious, and from my comments you should probably know that I oppose arbitration unless it is a final, binding step in dispute resolution. If arbitration isn't final, then I see no reason to have it at all, and if it isn't binding, then it is nothing but regular mediation.

There has been some criticism of the establishment of a standing ArbCom, but I wonder if that criticism is enough to prevent it's creation anyway. That point aside, what I am basically envisioning now is similar in spirit to your old proposal on ad hoc arbitration: A pool of qualified arbiters, from which a few neutral parties are selected in response to a specific dispute. We could then specify the rules and procedures for such an arbitration in policy, so that there was no confusion or ambiguity.

While I was opposed to your proposal initially, the political climate here has changed much since then, and hindsight is always 20/20. At least you've been far to polite to say "I told you so". --Whiteknight (talk) (projects) 15:50, 14 February 2007 (UTC)

Editorial board
So long as I am thinking about it, I wanted to ask for your opinion of the editorial board proposal. I think a formal board like this would really work wonders here, and help some of our better books get the attention that they really deserve.

I'm really excited about this proposal, and I really want to see it succeed. Any input would be appreciated. --Whiteknight (talk) (projects) 16:38, 14 February 2007 (UTC)

Arbitration Committees
I am opposed to a standing arbitration committee because the Wikibooks community is too small to ensure an impartial committee and so committee members should be chosen when needed and should always be non-biased and completely neutral (as much as possible). SBJohnny is one of the best Wikibooks members and admins but he is central to the Panic arguement and so can't be considered as completely impartial although I certainly wouldn't call him biased. I also didn't like the tone of the proposal which sought to incriminate Panic from the start and was dragging this issue on yet again with the threats of permanent blocks which, in my opinion, should only ever be used for blatant trouble-makers - we can probably all agree that Panic is not blatantly trying to cause trouble however much he may be at fault.

I'd prefer to see an end to this issue and for everyone incolved to exercise restraint for now. Failing that I'd agree to a restart of the original arbitration with Robert or someone else who is pretty neutral (or maybe Herby) taking charge. This whole issue is a mess and my actions were done with good intentions - others agreed that Panic should be unblocked (and reblocked for the original 2 weeks) but they felt that they were in a biased position and such a move wouldn't be possible. I am probably biased myself but I stand by my actions. Xania talk 21:23, 14 February 2007 (UTC)

 * The Panic problem might be showing that Wikibooks needs procedures. If we agree a constitution, or set of procedures, then everyone involved knows that the process is fair.  This in itself takes some of the heat out of a conflict. Your idea of collecting together admins for a particular case seems good to me.  We would need a set of procedures describing how this might be accomplished and the extent of their powers after they have formed an ad hoc group. RobinH 10:09, 15 February 2007 (UTC)

 * Considering the roll of arbitration, and the potential power it might have, we should likely only pick arbiters from the pool of currently active admins. Given that, I think the process could easily be modeled off the idea of jury selection: both disputants could go down the list of current active admins, and select admins that they don't suspect are biased against them. Any names that make it onto both lists will be eligible to be arbiters (the admins should probably have to agree to it first). This raises the problem of polarized situations where all admins are either biased or opt not to get involved, which will require some other sort of compromise. --Whiteknight (talk) (projects) 18:42, 15 February 2007 (UTC)

Front Page
The changes I made try to both reduce the size of the page, so its not overfull and trying to find a balance between readers and contributors. I think in the past the front page has tended to switch between focusing entirely on readers or entirely on contributors, when Wikibooks needs both in order to work. That said I've added 'By print version' to Search and Browse which links to the PDF versions page and added 'Good books' to Special Groups that links to Featured books page. I don't feel like its the right time to do much more than that, since there seems to be some debate as how to move forward with regards to publishing books, ways to improve existing books and ways to bring attention to good books that I believe will effect both of those pages. --dark lama  15:39, 16 February 2007 (UTC)

 * I think the addition of the "Featured Books" link in the sidebar should qualify in your request to have a link to our good books. We can add another link to that page if you want, but Frankly i find it a little embarrassing. The list is completely unmaintained, and (as i've said a million times before) there are books on that list that shouldn't be, and books that aren't on that list that should. If we had a list worth pointing to, I agree that a link to it should be posted right on the main page. --Whiteknight (talk) (projects) 19:21, 16 February 2007 (UTC)

 * I have transferred this discussion to the Staff Lounge.Staff_lounge RobinH 12:08, 17 February 2007 (UTC)

Main page
Thanks for support. I like the direction you have taken in your project, but nonetheless I don't like few things.

First of all, the table with "excellent books" (is "excellent" the best word? Aren't we exaggerating?) leaves too much space in left and right; this looks odd. Perhaps the solution is to make a two-column layout to use all of existing space? Look how long is the page now; it should be not like that, especially when category selection is deep on the bottom.

Secondly, I don't think that putting PDF's in front is a good idea. We are wiki and should be focused on wiki materials. PDF's are: inconsistent in look, require user to download a large ammount of data at once, may be seriously outdated and are something "external" to our project (internal links, categories do not work). I think that part of Wikipedia success is that you read and simultaniously fix mistakes you find. Showing out non-editable form of our books would be a shot in our foot in my opinion. So, the order should be the opposite: book titles should lead to books on our wiki (cover pages when possible), and links to PDF versions should be given as an option.

Less important things: table with Wikijunior books has an inconsistent look with the rest of the page. "Search and browse" with category selection together with list of sister projects leave to much white space on left and right. They should be aligned more horizontally; be wider but lower.

Things I particularly like are book descriptions with cover images; this brings some diversity to the main page. --Derbeth talk 15:28, 20 February 2007 (UTC)

 * Yes, we have to "lay out our stall" to be successful. I will continue this reply at Main Page/test..... RobinH 15:37, 20 February 2007 (UTC)

Opinion requested
I have been reading all discussion on the WB:DM (Decision Making), you seem to share some common views with me, I'm elaborating an essay that will try to address all relevant points, can you take a look on the essay and give me a notion on your level of concordance with it, that would be helpful to me. txs. --Panic 21:05, 20 March 2007 (UTC)

I have nominated you for admin
Just to inform you that I have done this in regards for your activity and involvement in the community, feel free to accept or decline the nomination. --Panic 18:28, 13 April 2007 (UTC)

 * Hi RobinH. Are you going to accept the nomination?-- SB_Johnny | talk 09:27, 24 April 2007 (UTC)

Concern about growth of Wikibooks
I want to let you know that I share your concern about the growth of Wikibooks and feel that the current direction that the "leaders" of Wikibooks have taken in recent months in response to issues that have been raised and abrasiveness toward new users and new ideas is directly related to the current decline in readership and overall growth of this project.

And for myself, I have been pushed off of the Staff Lounge and no longer feel welcome to post comments there, or really on nearly any page here on Wikibooks for that matter. I hope that changes and changes soon, and cosmetic changes such as the front page also not going to completely fix this problem.

I'm still watching Wikibooks, but I'm not going to be actively participating in much of anything for what I hope are obvious reasons to somebody who can read my user page. It looks like Karl Wick is coming back into the fray and going to try and make some changes. If he does, I would strongly urge you to treat him as if he was Jimbo. Seriously. While not completely of the God-King role that Jimbo was, if he wants to do a major cleanup of Wikibooks I guarentee that the WMF board will listen strongly to any suggestion he makes.

At the same time, Karl is not one to make huge waves and does an amazing job of concensus building. The main page is something he strongly looks at, and he was instrumental in making the front page what it was about a year ago when we did the last major overhaul of that page. If he steps into a leadership role and does some policy cleanup too (that isn't his style, but who knows), I might get involved here again in a more substantive way. And it will be a very positive experience for all Wikibookians. --Rob Horning 21:37, 13 April 2007 (UTC)

featured book nominations
I created a little template Featured book vote that you can put on a book that you've nominated to alert the authors and readers about the vote. Since you seem to be doing most of the nominating, i figured i would tell you personally. --Whiteknight (talk) (projects) 17:10, 19 April 2007 (UTC)

Introduction to Paleoanthropology
re: meta:User_talk:Tsca

Hello. I've had a look at Introduction to Paleoanthropology and it seems only 13 pages need to be renamed -- perhaps it's better done manually than with a bot? It only makes sense to employ the bot for mass moving/changes. If I misunderstood something please be more specific. // tsca [re] 19:26, 20 April 2007 (UTC)

 * Hey RobinH, I think i will take care of the page moves myself. I was worried about lots of inter-page navigation, but besides the one template I dont think it's going to be a big deal. I'll get started on it now, double check my work and make sure I dont miss anything. --Whiteknight (talk) (projects) 21:15, 20 April 2007 (UTC)

Books on Main page
Maybe we should start a thread about this issue on the staff lounge project chat or something, because alot of people seem to have many varied opinions on the issue and it's something that we should maybe discuss more publicly then on talk pages.

For myself, i think that putting more books on the main page then can fit without scrolling is a waste: the books at the bottom won't be seen as frequently and will be at a disadvantage compared to the books that are at the top of the page. The current system rotates the books in sets of 5 or 6 onto the main page each minute, so everytime the page is loaded it should show a new set of books. The disadvantage to this method, of course, is that many people may only load the main page once, and then open a book and start reading.

We could probably fit more books on there if we just listed the titles and included no pictures or descriptions (the way the main page was months ago), and I just dont feel like that's an acceptable option. --Whiteknight (talk) (projects) 14:52, 24 April 2007 (UTC)

Archive
Sure you found it by now but Featured books/Nominations/Archives -- Herby talk thyme 11:48, 25 April 2007 (UTC)

Special relativity, mathematical transformations
How do you get:

"But from the length contraction formula:

$$\frac{dt^'}{dt} = \frac {\gamma(u^')}{\gamma(u)}$$"

in the "Acceleration transformation" section? I think it needs a little bit of extra equations. Moriconne

 * Thanks for raising this, someone else put in this method originally but "length contraction" is a "bum steer"! I have fixed the derivation (see http://aether.lbl.gov/www/classes/p139/homework/eight.pdf for a Berkeley University source). There are definitely shorter ways of getting to the acceleration transformation but the expression above is interesting in its own right. RobinH 14:11, 15 August 2007 (UTC)

 * Thank you,the "length contraction" was sure a red herring. Very interesting and not so trivial :-) Moriconne

Special Relativity, General Cleanup
Hey RobinH, I wanted to do a little work on the special relativity book, and I figured I should give you a heads up about it all. I've created a page-header template for use on every page,. It's not the prettiest template, but it's better then how navigation was handeled before (every page had something different). I've also created a template for use on the TOC,. You can see the results of this template on the TOC now, in the few places where i've been able to use it. If you don't like this template, that's fine it is a little experimental.

I tagged the book with also, because some of the pages use a forward-slash convention and some of them use a colon convention. I want to go through and fix this, but I want to take some time and make sure I know where all the dependencies are so I don't create too many double-redirects. I also want to go through and make sure that the print version doesnt get all messed up. I won't be touching the LaTeX version or the PDF version or anything. Those can be updated later, if I make too many copyedits.

I really want to help this book out, so let me know if there is anything special that you think I should do while I'm feeling motivated to do it. --Whiteknight (Page) (Talk) 00:48, 14 August 2007 (UTC)

 * Also, there are a few orphaned pages from the old Modern Physics book that are about special relativity, and I am going to merge them into the special relativity book. A few of these pages have some images that will help the book as well. --Whiteknight (Page) (Talk) 01:00, 14 August 2007 (UTC)

Re:Hit counts
Teh only thing that I worry about is forcing people to load up an arbitrary amount of proprietary javascript. Making any kind of global change that forces people to load an unspecified amount of javascript (in addition to the mountains of code that some users already have) should be done cautiously. I'm not against google, and I'm not against the idea of getting a page count, but I would like to know what are going to be the performance side-effects, what are going to be the benefits, etc. If we ask people to "opt in" that would be one thing, but if everybody doesnt opt in, then the results would be no better then an alexa ranking. I'm not going to fight against the issue, but i have enough concerns to prevent me from pushing ahead at full speed. --Whiteknight (Page) (Talk) 12:33, 21 September 2007 (UTC)

 * I'm not entirely sure if i've done this correctly. Google analytics says they are "receiving data", but i wont receive any results until tomorrow. To join in my little test, add this to your javascript:

 * I'll let you know as soon as i get some results. --Whiteknight (Page) (Talk) 22:38, 24 September 2007 (UTC)

I just added the code for you. Your personal javascript page is located at User:RobinH/monobook.js. If you want to delete/modify the code, that is the place to do it. If you have any questions or comments, let me know. I will post results as soon as I get them. --Whiteknight (Page) (Talk) 12:07, 25 September 2007 (UTC)

 * No, code added on a book page won't be executed. The only way to get javascript to execute is to put it in your personal file, or to put it into a global file (such as MediaWiki:Common.js). I want to test the script for performance issues and accuracy issues. Once we test it, we can put the code into the global script so that all users will be running it.
 * Hopefully I'll be able to filter out the results to give me per-book results, which would be the most useful. We'll know as time goes on whether the effort is even worth it. --Whiteknight (Page) (Talk) 16:34, 25 September 2007 (UTC)
 * That sounds good. I am optimistic at the moment.   RobinH 08:27, 26 September 2007 (UTC)

Foundation members came down hard on my post to the mailing list. Nobody said it was a bad idea, but every body raised the same privacy concerns that darklama mentioned on staff lounge. Even for the case of just unregistered users, using the hit counter violates the privacy policy. There is some amount of hope, however, as my post seemed to get a couple people thinking about an alternative hit-counting mechanism.

The google analytics thing can stay active, but it's going to be strictly opt-in for registered users only. Nothing we can do about that. We could maybe try and come up with a home-brew page counting solution, but that would be a large effort. Sorry if this is disappointing to you (it is to me). --Whiteknight (Page) (Talk) 23:26, 2 October 2007 (UTC)

Wikicharts hit counter
Current address is: http://tools.wikimedia.de/~leon/stats/wikicharts/index.php?lang=en&wiki=enwikibooks&ns=all&limit=100&month=10%2F2007&mode=view

Original research
Please see Votes for deletion. Uncle G (talk) 13:18, 17 December 2007 (UTC)

Name
Hi RobinH

I'm just writing to let you know that I've changed my name from Urbane to Reece. Hope this doesnt cause too much confusion.

Reece  (Talk)   (Contributions)  15:10, 13 February 2008 (UTC)

Image:Constudtimeslit.gif is missing a fair use rationale

 * Rationale added - it is probably released as GFDL but I do not feel inclined to push the issue with the other originators of the drawing who are busy, working physicists. It could be replaced but I do not have time. RobinH (talk) 18:41, 5 June 2008 (UTC)
 * Would you take a look at Image:Rel4.gif as well? Thanks. — Mike.lifeguard | talk 04:59, 7 November 2008 (UTC)

Thanks
Thank you for supporting my request for adminship. It passed. Red4tribe (talk) 02:14, 3 July 2008 (UTC)

Deletions
Would you please provide a reason for as to why the following pages should be deleted by changing to  - thanks  –. ATALL/Input/References Urdu:Planning Wikipedia in the Classroom and Beyond Wikipedia in the Classroom and Beyond/How to use Wikipedia in the classroom Wikipedia in the Classroom and Beyond/Teaching Researching With Wikipedia Red4tribe (talk) 23:09, 16 July 2008 (UTC)

Can Quantum Mechanics explained by the twin paradox??
Hi RobinH, I know you contributed to the twin paradox in the Special Relativity Book.

I have a theoretical question: I know that the speed of light can not be reached, but let suppose that we are traveling on a space ship going at the speed of light. At the speed of light time stops. What happens when time stops? Does it mean that we are frozen, unmoved objects for eternity until we slow down, and time start again?

Lets say that we collide to an object in that high speed and our space ship split two halves, each continue going at the speed of light. Because time stopped for us, does it meant the split did not happened for us, we still be in one piece. For the observer however, we are two pieces. But when the observer ask a property of one of our halves, one halves also represent the whole, since the split did not happened for us.

Is this similar to the twin paradox?

The reason I am asking, it is not what we see when in Quantum Mechanics, in an accelerator, a particle is split apart and each travel a distance, and when we measure the property of one, the property of the other halves get known instantly, even if they are far away to each other. And It is unknown how could that information be there faster than the speed of light. Can it be explained by the twin paradox? The particle was split apart for us, but it was still one piece for the particle point of view, when the measurement of the property was made Ervinn (talk) 06:17, 17 September 2008 (UTC)

Hi Ervinn, I have not visited Wikibooks for several years, except occasionally to check on vandalism, so I missed your question. Particles with rest mass cannot reach the speed of light, although they might reach 0.999999..*c so if the split happened half way through a journey that registered 1 femtosecond on the spacehip's clocks there would still be 0.5 femtosecond either side of the split. However, there have been numerous attempts to link QM to relativity. Take a look at |The Transactional Interpretation of QM which is, so far, a theory that has withstood all challenges. RobinH (discuss • contribs) 10:47, 17 August 2012 (UTC)

Postulates of Special Relativity
Hi RobinH,

Thanks for your response to my comment about the SR postulates, and in particular about the role of symmetry in SR and the clock paradox. I look forward to hearing from you about the invariance of physical laws. Some of my comments were inappropriate and I have removed them. I am a total neophyte in Wikibooks so hope I'm doing it right and you get this OK.Cosmo (discuss • contribs) 22:41, 10 April 2013 (UTC)

I checked your response to my criticism of SR postulates and it seems that you condemn them as "incorrect". Please provide me with a little more detail of what is wrong. Can you just label it as incorrect and have it removed? Please let me know who makes the judgement call and perhaps we can take this further. Thanks. Cosmo (discuss • contribs) 21:30, 21 May 2013 (UTC)

I may have been a little premature in my comment as I'm not sure what you are referring to as "the amendment". So I will wait and see what changes you make if any.Cosmo (discuss • contribs) 03:54, 24 May 2013 (UTC)

Global account
Hi RobinH! As a Steward I'm involved in the upcoming unification of all accounts organized by the Wikimedia Foundation (see m:Single User Login finalisation announcement). By looking at your account, I realized that you don't have a global account yet. In order to secure your name, I recommend you to create such account on your own by submitting your password on Special:MergeAccount and unifying your local accounts. If you have any problems with doing that or further questions, please don't hesitate to contact me on my talk page. Cheers, DerHexer (discuss • contribs) 19:10, 14 January 2015 (UTC)

Origin of space time images.
https://en.wikibooks.org/wiki/File:Rellightcone.gif https://en.wikibooks.org/wiki/File:Coord3.gif

Hello Robin,

Could you please tell me, the background & where these images originated from, before they were uploaded?

Are they original works by you? If so I don't want them removed, I am just curious as I get a sense of deja vu seeing them.

(Semi)Anon.

title: User talk:RobinH


text: File:UI-Button.png

title: File:UI-Button.png


text: File:UI-Checkbox.png

title: File:UI-Checkbox.png


text: File:UI-Textbox.png

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text:
Template:High School Mathematics Extensions/Matrices/Linear Recurrence Relations Revisited

*Linear recurrence relations revisited*
We have already discussed linear recurrence relations in the Counting and Generating functions chapter. We shall study it again using matrices. Consider the Fibonacci numbers
 * 1, 1, 2, 3, 5, 8, 13, 21...

where each number is the sum of two preceding numbers. Let xn be the (n + 1)th Fibonacci number, we can write:

\begin{matrix} \begin{pmatrix} x_n\\ x_{n-1} \end{pmatrix} & = &  \begin{pmatrix} x_{n-1} + x_{n-2}\\ x_{n-1} \end{pmatrix} \\ \\ & = &  \begin{pmatrix} 1 &1\\ 1 &0  \end{pmatrix} \begin{pmatrix} x_{n-1}\\ x_{n-2} \end{pmatrix} \\ \\ & = &  \begin{pmatrix} 1 &1\\ 1 &0  \end{pmatrix}^2 \begin{pmatrix} x_{n-2}\\ x_{n-3} \end{pmatrix} \\ \\ &... \\ \\ & = &  \begin{pmatrix} 1 &1\\ 1 &0  \end{pmatrix}^{n-1} \begin{pmatrix} x_{1}\\ x_{0} \end{pmatrix} \\ \\ & = &  \begin{pmatrix} 1 &1\\ 1 &0  \end{pmatrix}^{n-1} \begin{pmatrix} 1\\ 1  \end{pmatrix} \end{matrix} $$ In fact many linear recurrence relations can be expressed in matrix form, e.g.
 * $$x_n = 2x_{n-1} + x_{n-2}; \ \mbox{if n} \ge 2$$
 * $$x_1 = 1$$
 * $$x_0 = 1$$

can be expressed as

\begin{pmatrix} x_n\\ x_{n-1} \end{pmatrix} = \begin{pmatrix} 2&1\\ 1&0 \end{pmatrix}

\begin{pmatrix} x_{n-1}\\ x_{n-2} \end{pmatrix} $$ and therefore

\begin{pmatrix} x_n\\ x_{n-1} \end{pmatrix} = \begin{pmatrix} 2&1\\ 1&0 \end{pmatrix} ^{n-1} \begin{pmatrix} 1\\ 1 \end{pmatrix} $$

So if we knew how to compute the powers of matrices quickly then we can work out the (n + 1)th Fibonacci number rather quickly!

Computing Powers Quickly
Note that from now on we emphasise if a matrix is a vector by writing an arrow on top of it.

Consider

A = \begin{pmatrix} 1 & -2\\ 1 & 4 \end{pmatrix} $$

\overrightarrow{x} = \begin{pmatrix} 2 \\ -1 \end{pmatrix} $$

\overrightarrow{y} = \begin{pmatrix} -1 \\ 1 \end{pmatrix} $$

Something interesting happens when you multiply A by either $$\overrightarrow{x}$$ or $$\overrightarrow{y}$$ (Try it). In fact
 * $$A\overrightarrow{x} = 2\overrightarrow{x}$$

and
 * $$A\overrightarrow{y} = 3\overrightarrow{y}$$.

Generally for a matrix B, if a vector w ≠ 0 (the matrix with all entries zero) such that
 * $$ B\overrightarrow{ w } = \lambda \overrightarrow{ w }$$

for some scalar λ, then $$ \overrightarrow{ w } $$ is called a eigenvector of B and λ the eigenvalue of B (corresponding to w).

This is a feature of matrices that be exploited to compute powers easily. Here's how, using A, x and y from above, we write the two pieces of information together in matrix form:

A\begin{pmatrix}\overrightarrow{x} & \overrightarrow{y}\end{pmatrix} = \begin{pmatrix}\overrightarrow{x} & \overrightarrow{y}\end{pmatrix} \begin{pmatrix}2 & 0\\ 0 & 3\end{pmatrix} $$ or written completely in numeral form

\begin{pmatrix} 1 & -2\\ 1 & 4 \end{pmatrix} \begin{pmatrix} 2 & -1\\ -1 & 1 \end{pmatrix}

=

\begin{pmatrix} 2 & -1\\ -1 & 1 \end{pmatrix}

\begin{pmatrix} 2 & 0\\ 0 & 3 \end{pmatrix} $$

you are encouraged to check the above is correct. What we did was we merged $$\overrightarrow{x}$$ and $$\overrightarrow{y}$$ into a matrix using each vector as a column, next we multiplied it by the diagonal matrix whose entries are the eigenvalue of each eigenvector correspondingly.

How to now exploit this matrix form to calculate powers of A quickly? We require a simple but ingenius step -- post-multiply (i.e. multiply from the right) both sides by the inverse of

\begin{pmatrix} 2 & -1\\ -1 & 1 \end{pmatrix} $$

we have

\begin{pmatrix} 1 & -2\\ 1 & 4 \end{pmatrix} = \begin{pmatrix} 2 & -1\\ -1 & 1 \end{pmatrix}

\begin{pmatrix}2 & 0\\ 0 & 3\end{pmatrix}

\begin{pmatrix} 2 & -1\\ -1 & 1 \end{pmatrix}^{-1} $$

Now to calculate An, we need only to do
 * $$A^n =

\begin{pmatrix} 1 & -2\\ 1 & 4 \end{pmatrix}^n = $$

\begin{pmatrix} 2 & -1\\ -1 & 1 \end{pmatrix}

\begin{pmatrix}2 & 0\\ 0 & 3\end{pmatrix}

\begin{pmatrix} 2 & -1\\ -1 & 1 \end{pmatrix}^{-1}

...

\begin{pmatrix} 2 & -1\\ -1 & 1 \end{pmatrix}

\begin{pmatrix}2 & 0\\ 0 & 3\end{pmatrix}

\begin{pmatrix} 2 & -1\\ -1 & 1 \end{pmatrix}^{-1}

$$

but inverses multiply to give I, so we are left with
 * $$A^n =

\begin{pmatrix} 1 & -2\\ 1 & 4 \end{pmatrix}^n = \begin{pmatrix} 2 & -1\\ -1 & 1 \end{pmatrix}

\begin{pmatrix}2 & 0\\ 0 & 3\end{pmatrix}^n

\begin{pmatrix} 2 & -1\\ -1 & 1 \end{pmatrix}^{-1} $$

which is very easy to compute since powers of a diagonal matrix are easy to compute (just take each entry to the power).

Example 1
Compute A5 where A is given above.

Solution We do

A^5 =

\begin{pmatrix} 2 & -1\\ -1 & 1 \end{pmatrix}

\begin{pmatrix}2 & 0\\ 0 & 3\end{pmatrix}^5

\begin{pmatrix} 2 & -1\\ -1 & 1 \end{pmatrix}^{-1} $$

A^5 =

\begin{pmatrix} 2 & -1\\ -1 & 1 \end{pmatrix}

\begin{pmatrix}2^5 & 0\\ 0 & 3^5\end{pmatrix}

\begin{pmatrix} 1 & 1\\ 1 & 2 \end{pmatrix} $$

A^5 =

\begin{pmatrix} 2^6-3^5 & 2^6-2\times 3^5\\ -2^5+3^5 & -2^5 + 2\times 3^5 \end{pmatrix} $$

Example 2
Let
 * $$B = \begin{pmatrix}

-13 & 28\\ -8 & 17 \end{pmatrix} $$ and its eigenvectors are
 * $$\begin{pmatrix}

2\\ 1 \end{pmatrix} $$ and $$\begin{pmatrix} 7\\ 4 \end{pmatrix} $$

Calculate B5 directly (optional), and again using the method above.

 Solution  We need to first determine its eigenvalues. We do
 * $$\begin{pmatrix}

-13 & 28\\ -8 & 17 \end{pmatrix} \begin{pmatrix} 2\\ 1 \end{pmatrix} = \begin{pmatrix} 2\\ 1 \end{pmatrix} $$ so the eigenvalue corresponding to
 * $$\begin{pmatrix}

2\\ 1 \end{pmatrix} $$ is 1.

Similarly,
 * $$\begin{pmatrix}

-13 & 28\\ -8 & 17 \end{pmatrix} \begin{pmatrix} 7\\ 4 \end{pmatrix} = \begin{pmatrix} 21\\ 12 \end{pmatrix} = 3\begin{pmatrix} 7\\ 4 \end{pmatrix} $$ so the other eigenvalue is 3.

Now we write them in the form:
 * $$\begin{pmatrix}

-13 & 28\\ -8 & 17 \end{pmatrix} \begin{pmatrix} 2 & 7\\ 1 & 4 \end{pmatrix} = \begin{pmatrix} 2 & 7\\ 1 & 4 \end{pmatrix} \begin{pmatrix} 1 & 0\\ 0 & 3 \end{pmatrix} $$ now make B the subject
 * $$\begin{pmatrix}

-13 & 28\\ -8 & 17 \end{pmatrix} = \begin{pmatrix} 2 & 7\\ 1 & 4 \end{pmatrix} \begin{pmatrix} 1 & 0\\ 0 & 3 \end{pmatrix} \begin{pmatrix} 4 & -7\\ -1 & 2 \end{pmatrix} $$

Now
 * $$\begin{pmatrix}

-13 & 28\\ -8 & 17 \end{pmatrix}^5 = \begin{pmatrix} 2 & 7\\ 1 & 4 \end{pmatrix} \begin{pmatrix} 1^5 & 0\\ 0 & 3^5 \end{pmatrix} \begin{pmatrix} 4 & -7\\ -1 & 2 \end{pmatrix} $$
 * so multiplying the right hand side out, we get

$$\begin{pmatrix} -13 & 28\\ -8 & 17 \end{pmatrix}^5 = \begin{pmatrix} 8-7\times 3^5 & 14(3^5-1)\\ 4(3^5-1) & -7+8\times 3^5 \end{pmatrix} $$

Summary -- compute powers quickly
Given eigenvectors of a matrix A
 * 1) Compute the eigenvalues (if not given)
 * 2) Write in the form A = PDP-1, where D is a diagonal matrix of the eigenvalues, and P the eigenvectors as columns
 * 3) Compute An using the right hand side equivalent

Exercises
1. The eigenvectors of
 * $$B = \begin{pmatrix}

-8&6\\ -15&11 \end{pmatrix}$$ are
 * $$\begin{pmatrix}

2\\ 3 \end{pmatrix}$$ and $$\begin{pmatrix} 3\\ 5 \end{pmatrix}$$ calculate B5

2. The eigenvectors of
 * $$B = \begin{pmatrix}

-8&6\\ -9&7 \end{pmatrix}$$ are
 * $$\begin{pmatrix}

1\\ 1 \end{pmatrix}$$ and $$\begin{pmatrix} 2\\ 3 \end{pmatrix}$$ calculate B5

3. The eigenvectors of
 * $$B = \begin{pmatrix}

177&-140\\ 225&-178 \end{pmatrix}$$ are
 * $$\begin{pmatrix}

4\\ 5 \end{pmatrix}$$ and $$\begin{pmatrix} 7\\ 9 \end{pmatrix}$$ calculate B5

Eigenvector and eigenvalue
We know from the above section that for a matrix if we are given its eigenvectors, we can find the corresponding eigenvalues, and then we can compute its powers quickly. So the last hurdle becomes finding the eigenvectors.

An eigenvectors $$\overrightarrow{x}$$ of a matrix A and its corresponding eigenvalue λ are related by the following expression:
 * $$A\overrightarrow{x} = \lambda \overrightarrow{x}$$

where x ≠ 0 where 0 is the zero matrix (all entries zero). We can safely assume that A is given so there are two unknowns -- $$\overrightarrow{x}$$ and λ. We have enough information now to be able to work out the eigenvalues (and from that the eigenvectors):

 * $$A\overrightarrow{x} - \lambda \overrightarrow{x} = 0$$
 * $$A\overrightarrow{x} - \lambda I \overrightarrow{x} = 0$$
 * $$(A - \lambda I) \overrightarrow{x} = 0$$

The matrix (A - λI) must NOT have an inverse, because if it does then $$\overrightarrow{x}$$ = 0. Therefore det(A - λI) = 0. Suppose

A = \begin{pmatrix} a&b\\ c&d \end{pmatrix} $$ then

A-\lambda I = \begin{pmatrix} a - \lambda&b\\ c&d - \lambda \end{pmatrix} $$

0 = \det(A-\lambda I) = (a - \lambda)(d - \lambda) - bc $$

Now we see det(A-λI) is a polynomial in λ and det(A-λI) = 0. We are already well-trained in solving quadratics, so it's easy to work out the values of λ. Once we've worked out the values of λ, we can work out $$\overrightarrow{x}$$ (see examples).

Example 1
Find the eigenvalues and eigenvectors of
 * $$A =

\begin{pmatrix} -4&15\\ -2&7 \end{pmatrix} $$ and then find D and P such that A = P-1DP.

Solution

We aim to find $$\overrightarrow{x}$$ and λ such that
 * A$$\overrightarrow{x}$$ = λ$$\overrightarrow{x}$$

we proceed

\begin{pmatrix} -4&15\\ -2&7 \end{pmatrix} \overrightarrow{x} = \lambda \overrightarrow{x} $$

\begin{pmatrix} -4 - \lambda &15\\ -2&7 - \lambda \end{pmatrix} \overrightarrow{x} = 0 $$ (**)

 * det(A - λI) =
 * 0 = (-4 - λ)(7 - λ) + 30
 * 0 = -28 - 3λ + λ2 + 30
 * 0 = λ2 - 3λ + 2
 * 0 = (λ - 1)(λ - 2)
 * λ = 1, 2

Now for each eigenvalue we will get a different corresponding eigenvector. So we consider the case λ = 1 and λ = 2 separately.

Consider first λ = 1, from (**) we get

\begin{pmatrix} -4 - 1 &15\\ -2&7 - 1 \end{pmatrix} x = 0 $$

i.e.

\begin{pmatrix} -5&15\\ -2& 6 \end{pmatrix} \begin{pmatrix} u\\ v \end{pmatrix} = 0 $$ where $$x = \begin{pmatrix} u\\ v \end{pmatrix} $$ since det(A - λI) = 0, we know that there is no unique solution to the above equation. But we note that:
 * $$x =

\begin{pmatrix} 3t\\ 1t \end{pmatrix} $$ for any real number t is a solution, and we choose t = 1 as our solution because it's the simpliest. Therefore
 * $$x =

\begin{pmatrix} 3\\ 1 \end{pmatrix} $$ is the eigenvector corresponding to λ = 1. (***)

Similarly, if λ = 2, from (**) we get

\begin{pmatrix} -4 - 2 &15\\ -2&7 - 2 \end{pmatrix} x = 0 $$

i.e.

\begin{pmatrix} -6&15\\ -2& 5 \end{pmatrix} \begin{pmatrix} u\\ v \end{pmatrix} = 0 $$ where $$x = \begin{pmatrix} u\\ v \end{pmatrix} $$ we note that:
 * $$x =

\begin{pmatrix} 5t\\ 2t \end{pmatrix} $$ for any real number t is a solution, as before we choose t = 1 as our solution. Therefore
 * $$x =

\begin{pmatrix} 5\\ 2 \end{pmatrix} $$ is the eigenvector corresponding to λ = 2. (****)

We summarise the result of (***) and (****), we have

A \begin{pmatrix} 3\\ 1 \end{pmatrix} = \begin{pmatrix} 3\\ 1 \end{pmatrix} $$

A \begin{pmatrix} 5\\ 2 \end{pmatrix} = 2 \begin{pmatrix} 5\\ 2 \end{pmatrix} $$

we combine the results into one

A \begin{pmatrix} 3&5\\ 1&2 \end{pmatrix} = \begin{pmatrix} 3&5\\ 1&2 \end{pmatrix} \begin{pmatrix} 1&0\\ 0&2 \end{pmatrix} $$ and so

A = \begin{pmatrix} 3&5\\ 1&2 \end{pmatrix} \begin{pmatrix} 1&0\\ 0&2 \end{pmatrix} \begin{pmatrix} 3&5\\ 1&2 \end{pmatrix}^{-1} $$

Example 2

 * a) Diagonalize A, i.e find P (invertible) and B (diagonal) such that AP = PB
 * b) Compute A5

A = \begin{pmatrix} 1&2\\ -1&4 \end{pmatrix} $$

 Solution a) We are solving Ax = λx, where λ is a constant and x′ a column vector. Firstly
 * $$Ax - \lambda Ix = 0$$
 * $$(A - \lambda I)x = 0$$

since 'x′ ≠ 0 we have
 * $$det(A - \lambda I) = 0$$

i.e.

\det\begin{pmatrix} 1-\lambda&2\\ -1&4-\lambda \end{pmatrix} = 0 $$

\begin{matrix} (1-\lambda)(4-\lambda) + 2 &=& 0\\ \lambda^2-5\lambda + 6    &=& 0 \end{matrix} $$

 * $$\lambda = 3,\ 2$$

For λ = 3,
 * $$(A-3I)x = 0$$

\begin{pmatrix} -2&2\\ -1&1  \end{pmatrix} \begin{pmatrix} x\\ y \end{pmatrix} = 0 $$

Clearly

\begin{pmatrix} x\\ y \end{pmatrix} = \begin{pmatrix} 1\\ 1 \end{pmatrix} $$ is a solution. Note that we do not accept x = 0 as an solution, because we assume x ≠ 0. Note also that

\begin{pmatrix} x\\ y \end{pmatrix} = \begin{pmatrix} t\\ t \end{pmatrix} $$ for some constant t is also a solution. Indeed we could use x = y = 2, 3 or 4 as a solution, but for convenience we choose the simplest i.e. x = y = 1.

For λ = 2,
 * $$(A-2I)x = 0$$

\begin{pmatrix} -1&2\\ -1&2  \end{pmatrix} \begin{pmatrix} x\\ y \end{pmatrix} = 0 $$

Clearly

\begin{pmatrix} x\\ y \end{pmatrix} = \begin{pmatrix} 2\\ 1 \end{pmatrix} $$ is a solution.

Therefore

A \begin{pmatrix} 1&2\\ 1&1 \end{pmatrix} = \begin{pmatrix} 1&2\\ 1&1 \end{pmatrix} \begin{pmatrix} 3&0\\ 0&2 \end{pmatrix} $$ is a solution and

A \begin{pmatrix} 2&1\\ 1&1 \end{pmatrix} = \begin{pmatrix} 2&1\\ 1&1 \end{pmatrix} \begin{pmatrix} 2&0\\ 0&3 \end{pmatrix} $$ is also a solution.

 * b)

A^5 = \begin{pmatrix} \begin{pmatrix} 2&1\\ 1&1 \end{pmatrix} \begin{pmatrix} 2&0\\ 0&3 \end{pmatrix} \begin{pmatrix} 2&1\\ 1&1 \end{pmatrix}^{-1} \end{pmatrix} ^5 $$

A^5 = \begin{pmatrix} 2&1\\ 1&1 \end{pmatrix} \begin{pmatrix} 2&0\\ 0&3 \end{pmatrix}^5 \begin{pmatrix} 2&1\\ 1&1 \end{pmatrix}^{-1} $$

A^5 = \begin{pmatrix} 2&1\\ 1&1 \end{pmatrix} \begin{pmatrix} 2^5&0\\ 0&3^5 \end{pmatrix} \begin{pmatrix} 1&-1\\ -1&2 \end{pmatrix} $$

A^5 = \begin{pmatrix} 2^6-3^5&2^6-2\times 3^5\\ 2^5-3^5&-2^5+2\times 3^5 \end{pmatrix} $$

Example 3
Solve the linear recurrence relation

\begin{matrix} x_n &=& 5x_{n-1}& -& 6x_{n-2}; \ \mbox{if n} \ge 2\\ x_1 &=& 1\\ x_0 &=& 0\\ \end{matrix} $$

 Solution

\begin{pmatrix} x_n\\ x_{n-1} \end{pmatrix} = \begin{pmatrix} 5&-6\\ 1&0 \end{pmatrix}^{n-1} \begin{pmatrix} 1\\ 0 \end{pmatrix} $$

We need to diagonalize

A = \begin{pmatrix} 5&-6\\ 1&0 \end{pmatrix} $$ we proceed:
 * $$\det{(A - \lambda I)} = 0 \!$$

we get
 * λ = 2, 3

For λ = 2
 * $$(A - 2I)x = 0 \!$$
 * $$x=

\begin{pmatrix} 2\\ 1 \end{pmatrix}$$

For λ = 3
 * $$(A - 3I)x = 0 \!$$
 * $$x=

\begin{pmatrix} 3\\ 1 \end{pmatrix}$$

Therefore
 * $$A =

\begin{pmatrix} 2&3\\ 1&1 \end{pmatrix} \begin{pmatrix} 2&0\\ 0&3 \end{pmatrix} \begin{pmatrix} 2&3\\ 1&1 \end{pmatrix}^{-1} $$

Now
 * $$A^{n-1} =

\begin{pmatrix} 2&3\\ 1&1 \end{pmatrix} \begin{pmatrix} 2&0\\ 0&3 \end{pmatrix}^{n-1} \begin{pmatrix} -1&3\\ 1&-2 \end{pmatrix} $$
 * $$A^{n-1} =

\begin{pmatrix} 2&3\\ 1&1 \end{pmatrix} \begin{pmatrix} 2^{n-1}&0\\ 0&3^{n-1} \end{pmatrix} \begin{pmatrix} -1&3\\ 1&-2 \end{pmatrix} $$

 * $$A^{n-1} =

\begin{pmatrix} -2^n+3^n&3\times 2^n-2\times 3^n\\ -2^{n-1}+3^{n-1}&3\times 2^{n-1}-2\times 3^{n-1} \end{pmatrix} $$

Therefore

\begin{pmatrix} x_n\\ x_{n-1} \end{pmatrix} = \begin{pmatrix} -2^n+3^n&3\times 2^n-2\times 3^n\\ -2^{n-1}+3^{n-1}&3\times 2^{n-1}-2\times 3^{n-1} \end{pmatrix} \begin{pmatrix} 1\\ 0 \end{pmatrix} $$

\begin{pmatrix} x_n\\ x_{n-1} \end{pmatrix} = \begin{pmatrix} -2^n+3^n\\ -2^{n-1}+3^{n-1} \end{pmatrix} $$ i.e
 * $$x_n = -2^n + 3^n \!$$

Exercises
1. Compute A5 where
 * $$ A =

\begin{pmatrix} -12 & 10\\ -21 & 17 \end{pmatrix} $$

2. Compute A5 where
 * $$ A =

\begin{pmatrix} -6 & 28\\ -2 & 9 \end{pmatrix} $$

3. Solve the following recurrence relations
 * $$x_n = 3x_{n-1} - x_{n-2} \!$$
 * $$x_1 = 1 \!$$
 * $$x_0 = 0 \!$$

 Solutions

1.
 * $$ A^5 =

\begin{pmatrix} -2922 & 2110\\ -4431 & 3197 \end{pmatrix} $$

2.
 * $$ A^5 =

\begin{pmatrix} -216 & 868\\ -62 & 249 \end{pmatrix} $$

More Applications
...more to come

Problem Set > High_School_Mathematics_Extensions/Matrices/Problem Set

Project > High_School_Mathematics_Extensions/Matrices/Project/Elementary_Matrices


text:
High School Mathematics Extensions/Matrices/Problem Set

Problem Set
1. Zhuo decided to write a message to Jenny using matrix encryption. He substituted each letter in the English alphabet with a number:
 * A to 0
 * B to 1
 * C to 2
 * Z to 25,
 * Z to 25,

he then wrote his message in a 2 by 4 matrix as follows
 * $$X =

\begin{pmatrix} ?&?&?&?\\ ?&?&?&?\end{pmatrix} $$, now he pre-multiplies his secret message X with a matrix to get the result

\begin{pmatrix} 2&3\\ 3&5\end{pmatrix} \begin{pmatrix} ?&?&?&?\\ ?&?&?&?\end{pmatrix} =\begin{pmatrix} 28&94&70&102\\ 44&153&112&163\end{pmatrix} $$.

What was Zhuo's message to Jenny?

2. A 2 by 2 matrix A has the following property
 * $$A\begin{pmatrix}1 \\ 2 \end{pmatrix}= \begin{pmatrix}1 \\ 0 \end{pmatrix}$$

and $$A\begin{pmatrix}3 \\ 4 \end{pmatrix}= \begin{pmatrix}0 \\ 1 \end{pmatrix}$$.

What is the inverse of A?

3. Let
 * $$J = \begin{pmatrix}0 &1\\ 1 &0 \end{pmatrix}$$,

and let K = I + J. Show that Kn = nK.

4. Suppose
 * $$A^k = 0 $$

and
 * $$B^l = 0 $$

prove or disprove that you can always find a positive integer m such that
 * $$(A + B)^m = 0 $$

5. Let p and q be two real numbers such that p + q = 1. Show that there is a 2 × 2 matrix, A ≠ I (i.e. not equal to the identity) such that
 * $$A\begin{pmatrix}

p\\ q \end{pmatrix}= \begin{pmatrix} p\\ q \end{pmatrix} $$

6. Find A such that: $$A^3 = \begin{pmatrix} -10&18\\ -9&17 \end{pmatrix} $$

''...more to come. Please contribute good problems''


text:
High School Mathematics Extensions/Matrices/Project/Elementary Matrices

Project -- Elementary matrices
Throughout, $$ A = \begin{pmatrix}a & b\\ c & d\end{pmatrix}$$

1. The matrices below are called elementary matrices. How are the matrices below different from the identity matrix I, describe each one.
 * $$\begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix}$$
 * $$\begin{pmatrix} 1 & f \\ 0 & 1 \end{pmatrix}$$ where f is a scalar
 * $$\begin{pmatrix} 1 & 0 \\ f & 1 \end{pmatrix}$$ where f is a scalar
 * $$\begin{pmatrix} f & 0 \\ 0 & 1 \end{pmatrix}$$ where f is a scalar
 * $$\begin{pmatrix} 1 & 0 \\ 0 & f \end{pmatrix}$$ where f is a scalar

2. In each of the cases, compute B then describe how is B different from A
 * $$B = \begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix}A$$
 * $$B = \begin{pmatrix} 1 & f \\ 0 & 1 \end{pmatrix}A$$ where f is a scalar
 * $$B = \begin{pmatrix} 1 & 0 \\ f & 1 \end{pmatrix}A$$ where f is a scalar
 * $$B = \begin{pmatrix} f & 0 \\ 0 & 1 \end{pmatrix}A$$ where f is a scalar
 * $$B = \begin{pmatrix} 1 & 0 \\ 0 & f \end{pmatrix}A$$ where f is a scalar

3. The matrix $$\begin{pmatrix}1 & 2\\4 & 3\end{pmatrix}$$ has determinant not equal to zero. We can decompose the matrix into products of elementary matrices pre-multiplying the identity:
 * $$\begin{pmatrix}1 & 2\\4 & 3\end{pmatrix} = \begin{pmatrix}0 & 1\\1 & 0\end{pmatrix}

\begin{pmatrix}1 & 3\\0 & 1\end{pmatrix} \begin{pmatrix}1 & 0\\1 & 1\end{pmatrix} \begin{pmatrix}1 & 0\\0 & 5\end{pmatrix} \begin{pmatrix}1 & -3\\0 & 1\end{pmatrix} \begin{pmatrix}1 & 0\\0 & 1\end{pmatrix}$$ Now suppose det(A) ≠ 0, can A be expressed as the product of elementary matrices and the identity?

4. a) Show that every elementary matrix has an inverse. Hint: use determinant.

b) Prove that every invertible matrix (a matrix that has an inverse) is the product of some elementary matrices pre-multiplying the identity.

5. A transpose of a matrix C is the matrix CT where the ith row of C is the ith column of CT. Prove using elementary matrices that
 * $$(DE)^T = E^TD^T$$

for arbitrary matrices D and E.

6. Show that every invertible matrix is also the product of some elementary matrices post-multiplying the identity.

7. How about non-invertible matrices? What can you say about them?