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Talk:Data Structures

General
This textbook aims to cover what CS majors learn in an introductory data structures and algorithms programming course.

Do we want to do everything for this subject on one page, or make this just a page of links? I like the second idea better.

''I prefer dropping new information here until a section gets "too big". Then split off that section onto its own page. See http://CommunityWiki.org/BigBucketsFirst --DavidCary 05:41, 12 Jul 2004 (UTC) ''

I agree with that article's logic. I'll copy the material from my linked list page back to this page, and work on it here. Later on, maybe we'll span off to other pages aka buckets. --Waxmop

 * I think the buckets right now are too small. I think it would be easier (because this is a textbook) to divide the book into chapters, and have each chapter be a subpage (if necessary). Anything finer grained than chapters would mean a lot of clicking and it would be easy to miss having a coherent voice in the book (both for contributing authors and for readers). But that's just my own feelings on the matter: I want these to seem like real books instead of just indexes to entries in the wikipedia. Mshonle 09:31, 1 Aug 2004 (UTC)

Format
I'd like to join the project if I may. I'm ready to tackle a couple of these topics. Is there a particular format to use?--Wcrowe 21:34, 1 Jul 2004 (UTC)

I would like to suggest a change in the order of the chapters. I would like to have Graphs moved before Trees, as a tree is simply a special case of a graph. Pesto 04:11, 28 August 2005 (UTC)
 * I see what you are getting at, but the question is What's the best didactic ordering? After all, linked-lists are just another form of graph, further, they are another form of tree, so why not discuss linked-lists last? But to be serious, I think tree traversal algorithms are easier to understand than graph traversal algorithms. And by also being more limited, trees provide a good introduction to the concept of graphs. MShonle 05:37, 28 August 2005 (UTC)

jump in!
If you write an article, you get to choose the format. Later on, people might improve the format, but at the beginning, we should just get out something and let people work on refining later. --Waxmop 17:15, 4 Jul 2004 (UTC)

We should use header markup (with the equal signs) rather than bullet markup. The header markup builds the table of contents. Also, we should put articles into the Programming:Data_Structures namespace for now. I'm starting a linked list article. --Waxmop 17:22, 4 Jul 2004 (UTC)

 * I agree: looking at a table of contents gives a better idea of what the book is like, and encourages more modifications and additions. I'm going to change the format to that. Mshonle 09:48, 1 Aug 2004 (UTC)

I dropped the variables and types section.
It links to a javascript page right now that I don't think is relevant. Everyone: remember to use the namespace Programming:Data Structures:your topic for your articles.--Waxmop 22:55, 5 Jul 2004 (UTC)

Wikipedia links are good, but...
This is a textbook, therefore, IMO, sections should use a how-to approach. You will immediately see that this differs quite a bit from an encyclopedic approach. I hope it is everyone's intent to teach these subjects, step by step, rather than just create a collection of Wikipedia links.

Page Structure
I'd rather not make a large change without some discussion, but it seems to me that the sorting portion should be moved to the bottom. I kind of visualize this page as three sections:

I wasn't planning on laying out the whole menu. I just meant to put in some examples, but I went further than I intended. I think that this breakdown gives us better control over presenting pros & cons of collection selections (Since the list selections are together and the stack selections are together), and is more consistant.

Primary Storage Types Single object allocation (used to implements linked lists, most trees, ...) Array (used to implement array list, most stacks, circular queues, ...) Secondary Storage Types Lists Common list operations & example Set(pos, val), Get(pos), remove(pos), append(val) Implemented as a Linked List Single linked list Double linked list Implemented as an Array List Stacks Common stack operations & example Push(val), Pop (, peek?) Implemented on a Linked List Implemented on an array Queues Common queue operations & example enqueue, dequeue Implemented as LinkedList Implemented as an array (circular, fixed size queue) Special cases Dequeues (What is this used for, by the way?) Trees & Graphs (isn't a tree just a special case of a graph?) Common tree operations & example add, get, remove Implemented as links (like linked list) Implemented in an array (Heap) Special cases Binary tree Balanced Quad tree Graphs Hash Tables ... How do I choose a data structure for a given situation? Sorts Big O notation Combinations ArrayList and Hashtable ...

--BillKress 23:06, 5 Nov 2004 (UTC)

 * Big O Notation should be discussed in front because it is used throughout the rest of the material. You should also include the discussion of Abstract Data Types and information hiding in fron too. -- Gdarwin 06:42, 7 Nov 2004 (UTC)

 * Hi Bill, sorry for the late reply. That structure looks much better, though I would put trees in a section before graphs, because the traversal concepts like inorder, preorder, and post-order (for binary trees) is really something separate enough. After queues should be heaps, aka priority queues, and then the heap sort. For graphs, depth-first and breadth-first should be covered. Below is what I suggest: MShonle 01:00, 21 Dec 2004 (UTC)

Introduction What is Data Abstraction? The Node The most elementary data structure Arrays Matricies: two dimensional arrays Insertion sort on an array Binary search on a sorted array List Structures Common list operations & example set(pos, val), get(pos), remove(pos), append(val) [not sure about these operations: what about next? or iterators?] [Perhaps discuss operations on Nodes, versus operations on the List itself: example, Nodes have a next operation, but the List itself has a pointer to the head and tail node, and an integer for the number of      elements. This view would work well in both the Lisp and OO worlds.] Doubley linked list Vectors (resizeable arrays) Iterators Operating on sequences without knowledge of the sequence itself Stacks and Queues Common stack operations & example push(val), pop, and peek Implemented on a Linked List Implemented on an array Common queue operations & example enqueue, dequeue Implemented as LinkedList Implemented as an array (circular, fixed size queue) Dequeues Trees Common tree operations & example add, get, remove Binary trees in order, pre order, post order traversals Balanced binary trees Iterators for trees Min and Max Heaps A tree implemented as an array! (not to be confused with the heap in memory) Percolation Heap sort Treaps: heaps where elements can be deleted by name Graphs Directed and Undirected graphs matrix and list representations Depth-First Search Breadth-First Search Topological sort Hash Tables Iteration order for hash tables by augmenting the structure - iterating over items in the order in which they were inserted - iterating over the items based on most-recently-used Sets Different implementations - lists, binary search trees, bit arrays, hashtables Disjoint Sets (operations: union, find) Tradeoffs between Data Structures Use asymptotic behaviour to decide, most importantly seeing how the structure will be used: an infrequent operation does not need to be  fast if it means everything else will be much faster

The content is designed to compliment the Algorithms text book (the idea is that the reader would cover the DS book first, then the Algo book, and then the Advanced Data Structures and Algorithms book that would pick up the more random and advanced ideas). Most importantly, I'd like to see each book be small enough that it can be read completely in one or two semesters. The more reference-based or encyclopedic content could be saved for either the Advanced book or the wikipedia. MShonle 01:00, 21 Dec 2004 (UTC)

Incoherent Structure
I agree. I find it odd that a lot of list based structures are currently placed under linked lists, when these structures can obviously be impleneted as an array.

Your layout looks good, but I was wondering if we can add a disccusion about big O notation. I see it used here, but where is it formally defined?

Gdarwin 16:13, 29 Oct 2004 (UTC)

Proposed structure has been modified. I'd still like to hear one or two more people say that they prefer this structure before I refactor.

--BillKress 23:04, 5 Nov 2004 (UTC)

Duplication for Array
Currently we have some 2 articles on arrays one here and one in Programming:Arrays. We should merge realy leavin only a short into here and move the rest off.

 * Programming:Arrays is only a redirect to Data Structures/Arrays. --Krischik 06:47, 23 August 2005 (UTC)

 * I think the DS book should only talk about the most basic form of arrays, that is, integer-indexed arrays. Many of the other topics currently mentioned, like associative arrays, won't make sense to the reader because they haven't read about hash tables (which use simple arrays and linked-lists) or binary search trees yet. The purpose of our story should be abstraction, abstraction, abstraction, and show how the complex gets built up from the very simple; not how the complex gets built up from things just as complex. MShonle 14:50, 22 August 2005 (UTC)

 * Speaking of integer based array: even that leaved the question of "which integer"? (See: Ada Programming/Types/array) . Before the almost assembler like C came out (and predended to be a higher language) it was almost part of the definition of a (real) higher language that you did not need to choose a register sized mashine word as array index. As such I belive that restricting an array index to "integer" is actualy a loss of abstraction. Abstraction for me means: away from computer implementation - closer to the live of humans. Example: Humans use arrays of (Jan, Feb, ... Dec) or (Mon, Thu, ... Sun) while computers would internaly use (0, 1 ... 12) or (0, 1, .. 6). Even if a human would choose a number to represent a month or day he would choose a 1 for Jan or Mon and not 0 as a computer would do. A higher programming language with better abstraction allow a more human like representation (i.E. using an enumeration type as as index) . The Psydo language used in Computer Science should allow for the highest abstraction - and an  should not be out of the question. --Krischik 06:47, 23 August 2005 (UTC)
 * I completely agree with you that allowing different index types allows for better abstraction. But we need to be careful about which abstractions we're talking about. The purpose of this book is to describe how one would get from embarrassingly simple, low-level abstractions into very precise, semantic-rich, high-level abstractions. To me, it would kind of be like arguing that the Hashtables chapter should use Perl, because Perl already has hash tables built-in. But the point is not to write the most elegant code examples; the point is to demonstrate computer science concepts. I find the idea very beautiful that in a language like Lisp, all you need is cons, car and cdr, and from there you can make lists, trees and graphs. Add in a very simple array, and you can make hashtables and matrices, et cetera... This is a very compelling story, and it can't be told as well if unnecessary elements are constantly added as side-notes. MShonle 14:24, 23 August 2005 (UTC)
 * (BTW, a deeper discussion of rich programming languages might be better suited for the Programming Languages book, or also possibly the Advanced Data Structures and Algorithms book. MShonle 21:09, 23 August 2005 (UTC))

Quicksort misconceptions

 * Since superceeded by the Introsort algorithm, the Quicksort algorithm can exact excellent performance on purely random data. It's worst performance, however, occurs on nearly-sorted or on sorted data, at which point Quicksort becomes completely impractical.

The above quote is incorrect. The original quicksort introduced by Hoare used random, not deterministic, methods to select the pivot. Thus, the kind of data input (random or ordered) wasn't important. It would only perform poorly on the very slight chance that the random selections were suboptimal. Some bad textbooks present some pretty poor ways of picking the pivots, but that is not the true quicksort.

I think it would probably be best not to present quicksort in the data-structures book at all because it's already half-way covered in the Algorithms book (currently the partition portion of quicksort is covered). I think Bubble sort probably shouldn't even be mentioned, as selection sort performs better and is easier to understand. For a data-structures book, Heap sort makes the most sense. Part of my hope is that we can keep both the data-structures and algorithms books simple (by covering only the most fundamental tools), and get into the more advanced material (e.g. introsort) in an Advanced Data-Structures and Algorithms book. MShonle 19:34, 20 Dec 2004 (UTC)

Moving forward
It looks like we've resolved many of the issues on this page. How would one go about archiving this talk page? MShonle 19:18, 30 Dec 2004 (UTC)

 * Create an /Archive 1 page and move the stuff there. Now that sub-pages are active /Archive 1 allways works ;-). --Krischik 15:31, 23 August 2005 (UTC)

Template Tricks
Here's the page structure I have for the Introduction, and I'd like to repeat it for the other chapters:

Computer Science:Data Structures:Introduction -- simple page that includes: a header , - i.e. a template ,       - another template a horizontal line a footer , - the same template as the header where the template is: Template:Computer Science:Data Structures:Introduction -- a simple page that REDIRECTS to     the page Computer Science:Data Structures:Introduction_content Computer Science:Data Structures:Introduction_content -- the article that includes the chapter's *real* content.

The idea of these template tricks is two fold:
 * 1) The navigation templates simply allow you to browse the book easier; and
 * 2) The _content templates allow the book to be viewed in two different ways: by-chapter, or all-chapters

The by-chapter view is the one shown above. The all-chapters view would be a page that would look like this:

... and so on, including all of the _content pages (indirectly, because the templates will redirect)

The indirection is neccessary in order to avoid the chapter navigation getting shown in the all-chapters view.

The idea behind the all chapters view is that people could print out the book easily. Anyway, if you see some weird things, like the above, that's the reason why. MShonle 19:47, 30 Dec 2004 (UTC)

Pseudocode
I've implemented the Stack ADT in a pseudocode that I'm proposing for the rest of the book. I used a literate programming approach in which the implementation is interspersed with prose describing it. The pseudocode for a somewhat more complicated ADT should probably be copied here and used for an example. The details of the pseudocode follow.

All blocks begin with a keyword (so far type and method) and end with a line containing end and the keyword. The pseudocode is sensitive to line endings, although a python-like use of ; to put two commands on the same line would not be unreasonable. Make sure you indent the contents of all blocks.

I use  to introduce a new type. I use the word "type" rather than an alternative like "class" or "structure" because this is a book on abstract data types, rather than object oriented classes, and the word "structure" is too long. I drew the angle brackets from C++ template or Java generic syntax. I think it is important to point out that abstract types are parametrized on other types. The type ends with  on its own line.

The data keyword declares a private data member. It is of the form. I am using the Pascal style of data typing (: to introduce the type of a variable) because there's already a keyword in front of the variable and this allows us to use type names with spaces in them. Data members (so far) can be accessed by their name alone in any member function. Possibly, we should follow python's lead and require a "self." in front of an access to clearly distinguish them from local variables.

method introduces a public member function/method. These are of the form. A method ends with  on its own line. If a return type is present, a return statement with the right type must terminate all calls of the function. Probably we should find a way to indicate that a method does not modify its object or an argument. You call a member function using the standard  syntax.

I'd like a for loop that allows iteration over either a numeric range with a possible stride, or over all members of a given set or sequence. Perhaps the following syntax: for i in 1..11 [step 2] # Does this loop for i=11 or not? for i in some_set Pattern matching should probably be allowed too: for (first,second) in pair_sequence

Discussion

 * A defense of explicit typing in our pseudocode: In a couple places, MShonle has suggested that this book's pseudocode should not use generics, instead leaving certain variables untyped. I respectfully disagree. While certain languages (Perl, Python, Lisp) allow programmers to omit the types, this makes the programmer have a firmer understanding of what type a given variable has at any time since the compiler won't catch mistakes. Since we're trying to teach new programmers, who probably don't understand types as well, the type of any variable in our pseudo code should be specified. Without generics, if a variable declaration has no type, the reader has to guess the type. A mapping ADT will have two types that can vary, and a Graph may have even more. Using templates/generics adds a little syntax but allows us to type every variable we use. MShonle, if I'm wrong about your position, feel free to delete this paragraph. --jyasskin 07:01, 24 Jan 2005 (UTC)

Old discussion from above:
 * We should include code snippets in as many different languages as possible along with pseudocode.
 * I'm not sure "as many" languages as possible is desirable. Certainly the current fad language could be used, or a language like it. I'm a fan of pseudocode that absorbs the benefits from several languages. But data-structures in Scheme versus Python versus Java/C# are going to be very different. At some point decisions will have to be made. I believe for the topic of data structures that something closer to C should be used, but organized such that it could "obviously" be turned into an object-oriented program. At heart, Data Structures is about making linked-list and hash-tables and ballanced binary search trees: it would seem silly to implement a linked list in a language that already includes full, built-in support of them. (However, these high level-languages could offer a lot: as they can help in the design of the interface of the structures; for example by using iterators.) The Algorithms book uses a more pure pseudocode language that offers excellent looping constructs and array slices: the reason being that showing low-level details detracts from the "hard part" of what the algorithm is (i.e., introducing implementation complexity on top of the inherent complex makes the story telling harder)Mshonle 09:45, 1 Aug 2004 (UTC)

 * From a teaching perspective i think that pseudocode for data structures is much much clearer than any implementation. I would suggest that code snippets be first done in pseudocode, and then possibly in actual language code (is there a way perhaps this could be on a different page, like an appendix or something?)  The pseudocode is the clearest way to learn the concept, which is pretty indepedent of language.  I think both functional and procedural data structures should be shown, as functional programming is becoming more mainstream, and this book is not simply a programming text, but a CS text, and they are theoretically very important. JustinWick 15:19, 12 Nov 2004 (UTC)

 * I have a suggestion from the Computer Programming Book: Just read the following 3 pages: Computer Programming, Computer Programming/Control, Ada Programming/Control. It's almost what JustinWick suggested.

On the history page, Krischik said: "(Discussion - pseudocode vs real language - why not both?)". Answer: We are taking that approach. If people want to supply implementations in C, Scheme, Python or Java they may do so, as an appendix (the sister Algorithms book has one appendix already set up, but with little work done on it). The pseudo-language is closest to Python, so it would be a good idea to test all of the samples by actually running them against a full test-suite (which should also be part of the appendix; see the Algorithms book). MShonle 14:35, 23 August 2005 (UTC)

Jyasskin said: "In a couple places, MShonle has suggested that this book's pseudocode should not use generics, instead leaving certain variables untyped. I respectfully disagree."
 * Thinking about this more, I think we probably should go with a light-weight kind of generics notation. Basically in the yellow "Some-structure Operations" boxes we could put the conventional  or  notations, just to say "when you see Key here, it could actually be anything". That probably would make things easier to read. This notation would only be used for the ADT descriptions. The methods themselves will just say "Key k" or "Element value", and when converting to a language, the reader will either: (1) delete the types, because it's a dynamically typed language; (2) enter in the generic notation, because it's a language that allows type parameterization; or (3) substitute for a concrete type, like string or integer, because the language doesn't allow for generics, but is also statically typed. MShonle 20:24, 29 August 2005 (UTC)

hi there! i just started reading this book, like it so far, but one thing conufses me: every chapter uses a diferent pseudocode; this realy makes it hard to follow...

TODO note
The references section should have its own _content page, so that it could be seen on the All Chapters view version of the book too. Possibily we'll want to do this for the preamble too. MShonle 20:59, 7 September 2005 (UTC)

reviews, quizzes?
Will this wikibook have reviews for each chapter, or perhaps quizzes, or even a test/project? I didn't really see any mention of this in the intro. Just wondering. I may be able to help with these. Gflores 02:24, 31 October 2005 (UTC)
 * Err... nevermind. I guess that's up to Data Structures on Wikiversity . It sure does seem like a lot of duplicate work... Gflores 00:41, 1 November 2005 (UTC)

still active?
I was just looking at the history of some of the modules and some date back to February. Is this book still active?

adding implementations
I noticed the part saying that implementations in various languages would be welcome as an Appendix. I agree that this is a good idea, and would be willing to add some of them. I'm not sure what a good structure would be. Have a page as the appendix with everything on it? A page as the appendix with links to pages for individual structures, featuring an implementation in each language, and/or links to pages for each language, featuring an implementation of each structure mentioned in the book. Any thoughts? Cat Parade 06:39, 8 March 2006 (UTC)
 * I agree completely. It would be great to have an appendix for code and pseudocode. I've noticed several sections that contain mostly code. The implementations are great but too much in the text will make a section unreadable. Christopher.Reilly (discuss • contribs) 12:05, 16 June 2015 (UTC)

Pages to merge
-- Adrignola talk contribs 13:39, 17 May 2010 (UTC)
 * Data Structures/merge Sort
 * Data Structures/bubble sort

 * I've merged the above striked out orphan to the relevant Algorithm Implementation page. The orphans don't fit on the scope of this book as they don't relate to data-structures per se. --Panic (talk) 02:12, 20 May 2010 (UTC)

Hash Trees
I would like to see the book cover Hash Trees regarding structures, traversal and uses. --Panic (talk) 02:31, 20 May 2010 (UTC)

Category template
Just a note for editors (and anyone doing administrative work) on the project's namespace. There is no need to add BookCat at all on subpages that already use the template (it is already included there). This also means you don't want the direct category addition below the template, which will upset the sorting that BookCat provides (would sort on D rather than H). This should probably be listed in a specific book convention page that explains what and how to use the navegation templates. --Panic (discuss • contribs) 09:42, 28 October 2011 (UTC)

title: Talk:Data Structures


text:
User:Cevans~enwikibooks

This is a test of the math code. For SU(3),

$$ 3 \otimes 3 = 1 \oplus 8 $$

--Cevans 00:23, 9 Jun 2004 (UTC)

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

title: User:Cevans~enwikibooks


text:
Lucid Dreaming/FAQ

This page is created solely for people to edit in any questions they may have regarding lucid dreaming. The authors (or others) can then post their answers (not necessarily definite—remember that we aren't author-ities *grin*). If you have a question, edit it in here and someone will try to answer it for you. And if you have an answer, by all means do contribute!

(Note: Although it's not necessary to sign your questions, always sign your answer!)

(Another note: Please preserve the alphabetical order of the FAQ.)

== When using the counting technique for induction, I always stop counting at some point and crash. The other techniques have their own little issues I can't work out (being a programmer, this really puts my nads in a salad shooter). Are there any computer programs I can run on a laptop that will somehow remind me that I am dreaming? == --Vampirism44 (talk) 22:59, 10 May 2009 (UTC) Yes, there are computer programs you can use. Just look at the software section in induction techniques. As for the counting technique, when you "crash", simply start counting from 1 again.

Lucidity has become chance for me, and even then it only occurs once every two weeks. Is there anything I can try to make it a 100% possibility per night?
== As lucid dreams are rare for me, this little bug really sucks. I gain lucidity, and when I try to give my dream a basic command (Like turning my hands blue, or making my sister explode), I wake up as the command takes effect. Even when I focus on something (my hands or the explosion), I wake. How do I combat this? ==

When doing some things (that wont work in real life) I sometimes start to slip out of it. What I do is just stop for a second (as the dream has become simply me with my eyes closed, imagining things) and just relax. Dont do any fast movements and soon you'll slip back into your little fantasy of blue hands and exploding siblings

Why do people want to move during sleep paralysis? I have had it about 3 times and have never tried to move.
Because for many of the people who experience this it is entirely accidental and so it is not a comfortable feeling at all. I have had sleep paralysis on roughly 4 occasions, all of them when I was younger except for one time around six months ago and none of them occured on purpose.

== I use the MILD, WILD, and counting induction processes at the same time. I experience sleep paralysis as "I'm breathing in, but I cant breathe out", and when ym lungs are full, it's REALLY uncomfortable. Also, if I stay this way for 20 secs, my entire room seems to twist, and I see a strange "screensaver" type thing. When I finally breathe out, everything clears, and I become lightheaded. Is there a chance that this is normal? ==

Probably. A lot of weird things happen during sleep paralysis (frequently including discomfort), and I've never heard of anyone actually getting hurt or dying because of sleep paralysis. Just relax.

Is it possible to use the WILD process with a little background noise? (Small pets moving in their cage, 20Db)
Some actually prefer to have some background noise. They concentrate on the noise, after some time, it becomes distorted.

I keep losing lucidity after I try to do something after "pausing" a lucid dream. How do I combat this? (Eg, pausing, then slapping the person in front of me, and I can't seem to lift my hand)
--Vampirism44 (talk) 00:29, 6 May 2009 (UTC) If you can't move your hand after slapping somebody, this is not losing lucidity. Rather, you probably regained the sense of your physical body and tried to move it rather than your dream body. To combat this, try focusing on the dream as much as possible and then try to move your hand. If this doesn't work, than try to genuinely believe that you will be able to move your hand in your dream, relying on the Placebo effect.

For how long do u have to experience the buzzing sensation in WILD before you become paralyzed?
anon: For me the paralysis goes pretty much hand in hand. After like a minute of buzzing I start to feel like I'm falling through my bed. If i try waking up after the "falling through my bed" has started, I almost every time end up having sleep paralysis. This freaked me out a lot of times in the beginning. Now, whenever i get the buzz, I just try to wait for it and let myself float away till my dream starts. Of course this could also be a placebo for me.

==A few of my normal dreams have had some good imagery, but none have had real vividness (e.g. proper sound, the brush of air etc.). I have not had a lucid dream, to the best of my ability, but am trying. Is it likely that a lucid dream would be more realistic in terms of my perceptions than a normal dream?==

Xgamer4: Not just likely. That's almost always the case. I'm not sure why that is though. One way to actually stay lucid is to, in-fact, focus on something in the dream. A wall, flower, plant, anything, and it helps keep you lucid.

Exabyte: I think that we don't remember normal dreams in much detail because we often don't pay much attention to those details (brush of air, fans running, etc.) in waking life, so our brains don't think to create them. When we are lucid, however, we often want to see how realistic dreams can be, so we look for details that we don't normally pay attention to. Thinking of these details causes our brains to create them. That's just my speculation, though.

Also, take into account that, although we perceive the world through the 5 senses, generally only one of them is the main neural path into the brain, so the other senses get, like, dimmed as our brain dedicates more resources to that main sense. What this means is that you can remember more of a dream's visuals but only some of the hearings, or more of the hearings but none of the touch; as a matter of fact, as far as I have known, few people remember the tastes of their dreams.

Ksd5: We don't remember normal dreams in much detail, because when we are sleeping, our memory receptors are not as active.

==Could someone please describe the sensation of sleep parilysis during WILD? Because I keep getting close to falling asleep while counting but I jerk myself awake because I suddenly think 'I'm gonna choke' or 'I won't be able to breathe!', And I want to be fully prepared for it.==

vodkeiro: I once had a sleep parilysis. I'm not sure if I was trying to have a Lucid Dream. What happened to me was that, I was having a nightmare, so I started to think loudly (inside the nightmare) "I wanna leave this place, NOW!". Suddenly, I woke up, I was in my room, and as it happens when someone has a nightmare, i tried to sit on my bed. There was the problem, I couldn't move, I "moved", but on the next second, I was again at the beginning, like when in a game, where you die and go back to the beginning as if nothing had happened. I tried to yell, scream, shout, everything, but nothing happened. After a few tries, I could move, but I was still a little scared. So, I don't think you'll think "I'm gonna choke", as you'll get really scared by not being able to move, so you're probably not thinking anything else.

Azmisov: Whenever I go into sleep paralysis my eyes start to flutter very rapidly and I see bright flashes of light. I have never had a painful deathly experience, although it can sometimes be a little uncomfortable. Usually, (I guess it depends on the person) it will last less that 30 seconds. This also depends on how fast you can transition into a lucid dream or astral travel.

When going into your dreams using WILD you may feel things like vibrations, falling and yes, choking.these are perfectly normal and more importantly safe. just stay calm and the feelings will eventually stop.

Alessandro (chemicalpoem@yahoo.it)

I have had lot of sleep paralysis, and I was very scared about it: gonna choke, gonna die, cannot move, arhg! But, after reading 'bout LD I got very interested in this phenomena and I started to wait fot getting it again. Just this night (I was very tired, it was 5o clock) it happened again. I just remained really quiet, enjoying this sensation: if you get sure that nothing is gonna harm you, 't's like a fantastic total body orgasm!Then I've had THREE consecutive LD, two false awakening and a long, long and very clear dream. So, just keep quiet and IMAGINE!

(sry if tis answer is not regular: I'm not english and I'm still euforic about the night!)

--118.92.27.198 (talk) 12:34, 18 December 2007 (UTC) I have experienced sleep paralysis a few times, the first time was after a lucid dream, I saw myself in a white bed with me(in reality I was sleeping on the couch) from side view, and didn't feel like moving untill after I woke up; I was 3/4 asleep so I didn't panic. the second time was after a non-lucid dream that ended in me pressing a red button, I heard strange highly pleasant music, felt emotions of euphoria and tranquility, and saw a scary, conspicuously sharp toothed monster leaning over me. The other times I don't remember. Everything I've read about sleep paralysis has said something different, so I guess it varies from person to person.

==For the last 3 years I have been getting what I thought was sleep paralysis, but since learning about lucid dreaming, I think my experiences are a form or at least a gateway to lucid dreaming. Is there a link between the two? (in short, i know that I am dreaming but often the dream is of me lying in my bed in my room, or a place similar to my room, so it can be confusing. It is unpleasant, as I feel a strong desire to wake up from the dream state but can't. I usually try screaming, or moving vigorously- i can't move properly or just roll off my bed(in the dream))==

Tharenthel: What's most important is to not doubt (even slightly) that you can move, and you'll be able to move. In a dream, whatever you believe you can do, you can do (though it can be hard to convince yourself of that sometimes). If you have trouble completely convincing yourself that you can move, you could try treating the dream sleep paralysis like real sleep paralysis. Use the WILD technique (while paralyzed in the dream) to separate your paralyzed dream body and a second "spirit" dream body (read the paragraph about sleep paralysis in the WILD section).

How good should your dream recall be before you attempt lucid dream induction techniques?
Xgamer: You should be remembering at least 1 dream every night though more is better. The main thing though is to just try when you are comfortable. Due to placebo you might get a lucid dream with less than that if you believe.

evilshiznat: Trying out the induction techniques is probably good while getting better at recall. It'll help you get used to it more, and once you get to one dream per night, you'll be all set.

KC: Developing your dream recall above zero is obviously necessary, but you better set your own pace. You could start trying the induction techs out right away, just don't be disappointed if you don't get immediate results.

I have difficulty telling the difference between dreams and reality - not during the dream itself, but when I remember things. Can I exploit this to induce lucid dreams?
Xgamer4: While I can't say I know much about it, having difficulty telling differences between dreams and real life in a memory happens to me also. It tends to be a common occurrence I think. It's even mentioned somewhere else here. On actually using it to induce a lucid dream, you could try incubating a dream. Other than that, I really don't know. Try stuff though and see if it works. If it does, tell us. If not, well, you tried.

==Is that possible to have a dream about having a lucid dream? I had a dream in which I had done a reality test and it showed that it was a dream. I walked through the wall, but I was too scared to jump from the window. In my nearly-lucid dreams I never think what I am doing, even when it is something strange. I just do. When I wake up, I often remember my dreams as if I were someone else watching myself in dream. Is that normal?==

--118.92.27.198 (talk) 12:42, 18 December 2007 (UTC) One question at a time mate. You cannot have a dream about having a lucid dream, that would be a lucid dream. I advise you to jump out of the window next time, doing something you are scared to do in a dream often has amusing results. It is normal to remember dreams as if you are someone else watching yourself, it's such a common feature in a dream that someone should come up with a name for such a dream.

I suggest you ignore the above comment, it is certainly possible to have a lucid dream about having a lucid dream. I can attest to this from experience. This will feel like a normal dream, which is what you seem to be describing. You may be aware that concentrating on a subject heavily will often influence your dreams - if you have been studying for a difficult test, you might have a dream about passing or failing it. If you have been recently been enjoying the company of a new girlfriend or boyfriend, they may appear in your dreams too. Likewise, if you have been looking into lucid dreaming and consciously focusing on it, you may have a dream that you are lucid dreaming. Don't read into it too much. --124.169.35.179 (talk)

==My dreams are often very realistic, e.g. I feel the wind blowing. But when I'm dreaming, I act like in a real life! I can't recognise my dreams that they are dreams. I've found out about lucid dreams about a month ago. I'm trying to have one, but I never had. What can I do to recognise my dreams as a dreams and have at last lucid dream? (Sorry for my English, I'm still learning! ;))==

Tharenthel: Other than trying some of the induction techniques, your best bet is probably to get in the habit of doing reality checks at certain times throughout the day. For example, you might do a reality check every time you wake up, use an elevator, or drive a car. It's best to choose events that happen frequently in your dreams, obviously. Keeping a dream journal will help your subconscious get used to any differences between your dreams and waking life (there probably are some subtle differences, even if you don't notice them), and improve your dream recall—you might have already had a lucid dream but just never remembered it! (I've had lucid dreams and not remembered them until hours after I woke up before, so it's definitely possible.) Also, if you have any books on lucid dreaming, reading one just before you go to sleep can help a lot since you'll be thinking about it as you fall asleep.

==Sometimes I've had dreams where I think I know I'm dreaming, but I still have limited control. I can never fly or anything, even though I actually try. Is there anything I can avoid just 'dreaming' that I know I'm dreaming?==

You must suspend all disbelief when attempting to do out of the ordinary things in a dream. Jumping off a building or a staircase is a good way to force yourself to fly. With time, you can just jump and fly wherever you want. Personally, during my first lucid experience, I couldn't move my body at all, but I got the hang of it eventually.

This almost seems religious, the idea of becoming your own god in your dream. What effect does Lucid Dreaming have on your spiritual life?
Xgamer4: I honestly can't say. Being Mormon, it doesn't seem to affect me very much. Mormons believe we were put on this earth to experience everything we possibly can in a life time and to return to living with the creators and helpers. To me, LDing, heck, just dreaming in general, is a way to experience many more things we couldn't experience in real life. I mean seriously, in real life, when are you going to get to fly around the world freely, or get chased by some scary thing then confront it, and it tells you why it's chasing you, or be chased by a lion in the middle of a jungle, or talk to people about anything while not worrying about being embarassed or ashamed of what you did, or etc.?

KC: Lucid dreaming in itself will not have an effect on your spiritual life, unless you want to use it for such a purpose (soul-searching and such). However, fear is one of the biggest obstacles in your way to lucid dreaming, and so are negative expectations. You are the person who controls your spiritual life, but if you need counseling, seek it from a proper representative of your own religion. My personal advice would be to drop any extra religious/spiritual baggage before you try lucid dreaming, but it's your choice.

[Gene] Lucid Dreaming is an essential indicator of higher awareness in many spiritual systems. See Ken Wilber, Buddhism, Ramana Maharshi. The ability to remain self-identified in dreaming sleep and (non-dreaming) deep sleep indicates awareness of higher bodies, the subtle self and the causal Self, respectively. This is normally achieved only after many years of meditation (which itself can be said to be a practice of release from object-relations). Dreaming sleep is a subtle body (mental) experience and deep sleep is a causal body (spiritual) experience. Most people associate their waking state awareness as "consciousness", but this is a consciousness that is formed in a context of object-relations, which objects help to identify "me" and "not me". When there are no perceived (external) objects, such as in deep sleep, can you identify your Self? It is a milestone of human development when infants achieve object constancy (maintain awareness of where an object is even if it is no longer in view), and is is also a milestone of development, though rarely achieved, to maintain self awareness even in the midst of no perceptions, ie. deep sleep. (e.g. even in a sensory deprivation chamber, one can perceive or feel their body). Ramana Maharshi (probably acknowledged as a true spiritual adept across more religions and spiritual disciplines than anybody) said "if it's not real in deep dreamless sleep then it's not real" meaning only that the highest causal Self (god) is real, and that the rest of typical human experience is transitory.

[b77] Expanding on Gene's comment above, I fully agree that restoring your self-awareness and retrieving your own identity during the LD is another milestone for humans' mental development. While I am deeply not convinced about any spiritual claims (religions and alike) and while I always try to find a 'scientific' reason for their existence, I believe that there is truly more to this universe than the science can account for or can 'reasonably' accept as plausible. So, if indeed death is not just The End, then the mere practice of restating/redefining yourself while in the middle of a LD would pave the way to controlling your death experiences, when the time comes. ...that is, if you're lucky enough to have time to prepare yourself... In other words, just as we have so much difficulty escaping those 'serious' nightmares—simply because we're not aware of their virtuality—I believe that whatever godly or ungodly experiences one may have on their final minutes are eventually conditioned by one's expectations and beliefs (see placebo question below). So, I would say that practicing LD and also keeping an eye on your own ideas and expectations about the other world could actually ensure a nice last trip out of here. And well, I would be happy to know that someone who is afraid of hell, of devils and alike, could eventually become aware that, whenever and wherever you may be, the one thing that cannot be destroyed in any way is your being (and staying) aware of yourself, as well as finding a single untouchable spot of self in the middle of whatever 'happens' around you. As someone who had to learn at some point to ignore an awful durable physical pain just to avoid losing mind, I eventually realized that a mental barrier between the self and the rest (including body), as hard to make and maintain as it is, may be the only apparent solution in such extreme cases. So yes, do play with LD, play it safe, don't ask too much too fast, and you'll surely be more than happy about your new invisible power :)

What are the benefits of lucid dreaming (aside from achieving personal interests)? Are there any negative aspects?
Question asked by Ivlarx 09:40, 24 Jan 2005 (UTC)

R3m0t: On the forum I frequent, LD4all, there is a large bias towards people who "just wanna have fun" (eheh) in their dreams. Popular targets include sex, flying, and shapeshifting.

There are stories in Exploring the World of Lucid Dreaming of people who found their dreams realistic enough to rehearse speeches, or create baking recipes. There were also stories that simply becoming lucid was an extremely fun experience in itself.

A small amount of people have overcome the fears from their nightmares in their lucid dreams. The chapter about it in EWLD (the book) is available as a free sample here.

Finally, there are people who use lucid dreams as a springboard to reach shared dreams (or "dreamwalking"), precognitive dreams, out-of-body experiences, and astral projection. I'm not sure myself why they want those (I imagine out-of-body experiences are fun because you can see your own body) but apparently some people do. I don't believe in shared and precognitive dreams myself and I also don't believe that out-of-body experiences and astral projection really are due to something (spirit, soul?) moving away from your body.

As for negative, I think that the section in ../Introduction covers that very well. The only thing it omits is obsession. ;) r3m0t (cont) (talk) 07:34, 27 Jan 2005 (UTC)

One negative thing is it's harder to be an early riser. You want to sleep more. CannibalSmith (talk) 16:13, 5 January 2008 (UTC)

What is the placebo effect?
The placebo effect occurs when something happens just because you believe it will. It strongly affects the nature of lucid dreams.

I suffered nightmares for many years (a result of abuse as a child), although they declined in my thirties. In my forties I began to become aware when a dream was beginning to turn into a nightmare, now 3 things can result from that lucidity: 1. My most satisfactory result is when I can I alter/divert the next stage of the dream, and it continues without nightmare; 2. I have difficulty diverting the dream sequence but tell myself I must wake up, and do; 3. I cannot just wake up, but I know I need to ask for help. I make myself speak/moan, which takes a lot of effort within the dream, but it always wakes my husband, who then wakes me up.

When I try to use the WILD technique, I feel a stron urge or tiredness to stop concentrating and go to sleep. Is this normal? It happens early when I first start.
--118.92.27.198 (talk) 12:54, 18 December 2007 (UTC)This has happened to me when I tried holding my arm up to keep myself awake. Is that what you are doing? Maybe you are staying too awake, In that case you should relax and let your "awareness" drop, try to find out how aware you need to be before your awareness drops so far you fall asleep, and aim just above that level.

Which site would you recommend to go to to discuss lucid dreams and such?
KC: Take a look at the newsgroup alt.dreams.lucid too. If you're not familiar with the Usenet, you can reach it via Google Groups.

r3m0t: I'm a frequent poster on LD4all. Unfortunately, LD4all has a few problems - the site is sometimes slow, the forum categories are less than perfect and there are plenty of repeated questions and postings (this is partly why the wikibook exists).

Xgamer4: I'd recommend LD4all. It has many forums to discuss with many other LD'ers. In fact, this wikibook is mainly the product of the board-goers at LD4all.

==it's possible to dream inside another dream?, I remember long time ago a lucid dream where I was in my home, then I tried go to bed to try sleep but when I tried to do that the dream ended spontaneously...==

It is possible to dream that you are dreaming, or to even dream that you have a lucid dream. The difference between dreaming you are lucid and actually being lucid is the fact that when not actually lucid, you have no control over the dream. However, I am unsure if it is possible to have a dream in which you go to sleep and continue a different dream. Dylnuge

Something like this happened to me. It felt like a normal dream, but i knew that i was dreaming. I had superpowers and this, but i couldn't control my dream.

I had somehing odd happen to me. Many years ago I awakened as usual one morning. Everything looked and sounded as it should. My wife was still sleeping. When I looked at her again, she started shapeshifting, an obvious absurdity in reality. I was speechless and shocked. Suddenly I realized I was dreaming and greatly relieved. I woke up, got out of bed, went to the bathroom and something made me realize I was dreaming yet again. This was in a way more shocking than the first false awakening because it was all so real and I wondered how far could this regress. At that point I awoke and found myself still in bed. This time I was not dreaming. A false awakening has never happened since.

i wanted to experience the OBE thing... how am i supposed to do that???
Azmisov: Many of the techniques shown here can be implemented into an OBE/astral travel experience. OBEs usually involve experiencing vibrational forces going through your body. (you should check out the Monroe Institute for more info on this) Another method is to just imagine yourself slipping out of your body. I really don't know if this technique is true OBE, it may just be another lucid dream. There are a lot of other methods I don't know about, so you can do some research to find more techniques.

==My occurrence for lucid dreaming varies from week to week, is this normal? For some weeks I can lucid dream everday for a week straight, then all of a sudden I can't for a month. Lately i have been able to lucid dream twice a night, sometimes three. Any clue what may cause this? Also when I do lucid dream a lot more, I act normal in a dream. I know I am dreaming, I can fly around, i can spawn things around me, but I still talk to people as if It was a real conversation.==

 Whether or not you were lucidly dreaming depends on whether you decided in your dream to fly, look in the mirror, etc. or whether you were only passively observing these events taking place in the dream. Realising you are in a dream and then remaining in the dream is a good sign that it was, as often the realisation you are dreaming is enough of a shock to wake you up, but the real test is your level of control. As far as not being able to swallow is concerned, if you were getting sick, especially if you were getting a temperature or something then this can also affect the vividness of your dreams.

====I have good dream recall, and when I sleep I never seem to lucid dream. When I am dreaming, really weird stuff happens to me. My mind never questions the bizzare circumstances I am put in. I have tried thinking that "I will have a lucid dream" over and over, and done some reality checks during the day. It never occurs to me to do them when I dream. Is there some way that will make me lucid dream for sure? Am I incapable of Lucid Dreaming?==== —Eponymous Anonymous

Li - I know what you mean. I've been trying every way to get a lucid dream, but nothing works. It sucks. I sometimes get really close but freak out and wake up. But despite my inexperience, I know for sure that everyone is capable of lucid dreaming. Try doing a wider variety of reality checks maybe, or perhaps try a different technique. What technique are you using?; WILD and VILD need lots of practice.

Walter Lewin 11:57, 13 November 2007 (UTC) - Yeah, I tried to do WILD for the past few weeks. Only once i felt a heavy pain in my chest, I found it hard to move but i could open my eyes and I woke up soon without dreaming lucid :(

--118.92.27.198 (talk) 13:07, 18 December 2007 (UTC) The correct way to do the MILD method is to go to sleep believing that you will "remember" that you are dreaming. Also, one key difference between lucid dreamers and non lucid dreamers trying to lucid dream is that lucid dreamers do not wonder if they are incapable of lucid dreaming, do not think that it never occors to them to do reality checks when they are dreaming, and tend to treat the phase "I did not lucid dream last night" as similar to the phase "I did not sleep on the couch last night", in other words, they tend to see lucid dreaming as something they can choose to do if they want to, rather than something they want to successfuly achieve at (long) last. -accepted-

==Is there a good method to remember your "waking" memories in a dream? Every time I get a dream I have control over myself, but I do not seem to know that I am in a dream and I cannot remember anything from when I am awake(therefore I can't do reality checks or anything "supernatural"). Any ideas of what I should do?==

==Is it possible to recall all waking memories in a lucid dream? I have had only two lucid dreams so far. I know these were lucid, because I did reality checks with positive results. I even managed to fly, create items, and etc. However, I couldn't recall a great deal of my waking memories. This cause me to lose lucidity half way through the dream.==

In your book (en.wikibooks.org/wiki/Lucid_Dreaming) you've mentioned a forum www.lucidforum.net which doesn't seem to be opening AT ALL. It's on the internet and it kinda doesn't seem to exist.. What do I do?

title: Lucid Dreaming/FAQ


text:
User talk:4.7.227.62

Vandalism on Cookbook:Rice
Dear 4.7.227.62:

Would you mind not vandalising Wikibook pages?

You have two more chances

Thank you,

EuropracBHIT 02:42, 9 Jun 2004 (UTC)

Vandalism on Cookbook:Allspice
Dear 4.7.227.62:

Would you mind not vandalising Wikibook pages (and a little politeness wouldn't hurt either)?

There are more interesting F-words in the cookbook: like fennel and flavour and flan.

You have one more chance.

Thank you, EuropracBHIT 02:47, 9 Jun 2004 (UTC)

title: User talk:4.7.227.62


text:
User talk:4.27.208.92

Hello 4.27.208.92

I don't know whether you're a new user or not (or one who has forgotten to log in!).

I appreciate the organisation of the Wikiversity and your contributions to the various Schools, in particular Art and Design and Medicine.

Thank you,

EuropracBHIT 02:51, 9 Jun 2004 (UTC)

title: User talk:4.27.208.92


text:
User:1234~enwikibooks

Hello

Hi!--Hyperlink 09:42, 18 Mar 2005 (UTC)

title: User:1234~enwikibooks


text:
User talk:66.119.33.186

Shakespeare's Romeo and Juliet: Act 3, Scene 1
Hello 66.119.33.186

Checking through KPJas's version and yours (as well as the current edit),I believe you were responsible for the 'amusing edits' to make a modern Shakespeare.

Correcting them to the way Shakespeare himself wrote them is a lot of work, and could well be constituted vandalism.

The reason this text is on Wikibooks is so that we can have the words as Shakespeare wrote them, which is very useful to students and teachers the world over.

Thank you,

EuropracBHIT 03:20, 9 Jun 2004 (UTC) who has a Complete Works of Shakespeare beside

title: User talk:66.119.33.186


text:
User talk:66.119.34.58

Hello 66.119.34.58,

Your alterations to Shakespeare's Romeo and Juliet (made on the 9th June) could be considered more than a little vulgar.

I do not think in Elizabethan times any character would be sitting on the john.

I have deleted all references to the john, and also 'after you here[sic] what Benvolio has to say'.

Please refrain from vandalising the work of Shakespeare,

EuropracBHIT 03:29, 9 Jun 2004 (UTC)

title: User talk:66.119.34.58


text:
User talk:66.119.33.185

Talk Romeo and Juliet Act III Scene III (Friar Lawrence's Cell)
Hello 66.119.33.185:

Would you mind not adding your comments to that they completely oblierate what is said about this scene and this act?

This could be construed as vandalism.

Thank you,

EuropracBHIT 04:10, 9 Jun 2004 (UTC)

title: User talk:66.119.33.185


text:
User talk:216.148.246.155

Romeo and Juliet, Act 3, Scene 3
Dear 216.148.246.155:

Would you mind not deleting the text of the act and scene, and putting in irrelevant material?

The Friar Lawrence scene is one of my favourites. I find it particularly effective in the Baz Luhrmann version, but Shakespeare's version is terrific too.

If it wasn't for it, we wouldn't be here!

Thank you,

EuropracBHIT 04:19, 9 Jun 2004 (UTC)

title: User talk:216.148.246.155


text:
Human Physiology

Contents

 * 1) /Physiology Introduction/
 * 2) /Homeostasis/
 * 3) Cell Physiology
 * 4) /Integumentary System/
 * 5) /The Nervous System/
 * 6) /Senses/
 * 7) /The Muscular System/
 * 8) Blood Physiology
 * 9) The Cardiovascular System
 * 10) /The Immune System/
 * 11) /The Urinary System/
 * 12) The Respiratory System
 * 13) The Gastrointestinal System
 * 14) /Nutrition/
 * 15) The Endocrine System
 * 16) The Male Reproductive System
 * 17) The Female Reproductive System
 * 18) Pregnancy and Birth
 * 19) Genetics and Inheritance
 * 20) Development: Birth through Death
 * 21) Appendix 1: Answers to Review Questions
 * 22) Authors
 * 23) Further Reading

title: Human Physiology