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Talk:Logistic function

Supremum link
INCORRECT LINK I believe the "Supremum" link is misassociated. It goes to "Infimum" instead of "Supremum". — Preceding unsigned comment added by 67.42.51.73 (talk) 21:14, 21 January 2023 (UTC)

 * The "Supremum" link is correctly linked to the page Supremum, which is redirected to the page Infimum and supremum. — Andy Anderson 22:48, 21 January 2023 (UTC)
 * I meant ... the "hover" link goes to Infimum rather than Supremum. Don't know if that is improvable or not. 67.42.51.73 (talk) 03:06, 22 January 2023 (UTC)
 * Default Wikipedia behavior, unfortunately. The hover displays the first paragraph of the linked page, and the supremum description is in the second paragraph. I merged the two paragraphs, and now at least part of the description shows up. — Andy Anderson 04:20, 22 January 2023 (UTC)

Notionational differences and different forms
I am having some problems w/ getting this correct, and it is very clear it has been three decades since I took calculus!

 * NOTE: Notation variation is common in this ubiquitous function, particular as it defines a wide range of natural system behavior over time.
 * Logistic growth (where this is the model of a population size), one of the most commmon applications of this function, is a function of time, so other sources may use $$t$$ as the variable, and $$x$$ to represent the population size. Also, some sources represent the population size (i.e. the y value) using pₜ (to incidate popuation of p at time t, with p₀ representing the initial population, i.e. at t₀
 * Logistic growth, when it is represented as a function of time, often will $$N$$,$$N_t$$, $$P$$, or $$P'_t$$ to reprsent the y value.
 * Other sources using other constants, e.g. both $$K$$ and $$M$$ are used fairly frequently for the carrying capacity (maximum population size a system can support).
 * Finally, the coeficient of the exponent also is frequently represented with r, and much less often, with μ, rather than k.

$$ N_{t} = \frac {K N_0 }  {N_0+({K-N_0})e^{-rt} } $$ which (well, should be) is the same as
 * So the above can be seen as:

$$ N_{t} = \frac {K N_0 e^{rt}} {({K-N_0}) + {N_0 e^{rt}}} $$

and

 * Where:
 * Nₜ is the population at time = t
 * K is the Carying capacity
 * r (the variable name used by Fisher in The Genetical Theory of Natural Selection) is the Population growth rate
 * t is time (note: must be of same magnitude/units as in r)

Some authors disregard convention and stick to x and y with a,b, and c as various constants.

Question: Should we add discussion about what happens w/ r>3???
The behavior of logistic growth, the stable basis of how most everything in the Universe seems to function, becomes rather interestng as r hits about 3, as seen on every article written about the Logicistic map showing its Bifurcation diagram.

We go from a very simple curve that underlies all living systems at multiple levels of emergence, radioactive decay, chemical kinetics, the spread of conspiracy theories, etc. to a great example of chaos theory. Initially, you see behavior that looks exactly like what we see in nature: a bit of an overshoot of K, with some ocilations around N=K until it settles down after a few periods. Crank it up a bit more and you start making fractals. The solution for this complex/chaotic behavior from a simple function is non-trivial and probably deserves some discussion by someone who is a bit fresher on the math

Its very telling, and worth discussion, that such a fundamental, and simple, eqution which underpins much of our experienced University resuts in chaos and while I don't want to introduce anything about butterfly wings in this dicussion, the impact of this behavior is real and inevitable. DrKC MD (talk) 04:11, 2 February 2024 (UTC)

Logistic Equation Page
I have to edit / make a wiki page for a project. I proposed to make a page titled Logistic Equation The page will basically link to here if people are looking for it continuous version (Logistic Differential Equation) and to the logistic map page if people are looking for its discrete form. Unless of course there are major objections from people. I feel the Logistic Equation is worthy of a page on its own as if you type logistic equation in google the mathworld page comes up first on the search. —Preceding unsigned comment added by Rjor2 (talk • contribs) 12:51, 19 February 2010 (UTC)

Notice on restructuring
I have reorganized the first two sections of the article. Please note that no (substantial) material has been deleted.

I now propose to make small textual additions in order to make the material (a) more accessible and (b) self-explanatory as much as possible. For example, It models the S-curve of growth of some set P. As a "pure" mathematician, the phrase "some set P" is delightful. But it might as well be "some set T" or "some set A" or "some set Z". That "P" is used is also self-evident because we made it so in the body of the entire article. Later we will want to reference Pierre François Verhulst. In that Wikipedia article the logistic differential equation uses the variable N. Such variety in variable names is acceptable to mathematicians and others of that ilk. But for the majority of Wikipedia readers, some explanation is needed.

The new text will read It models the S-curve of growth of some set P, where P might be thought of as population. This minor addition I will make now. --Михал Орела (talk) 07:29, 19 October 2008 (UTC)

The next text needing a massage is A logistic function is defined by the mathematical formula: The well-versed mathematical reader will understand that we are dealing with just one of the many mathematical forms in which the logistic function may be presented.

In particular, we will need to explain this particular choice and then to say later how it relates the wider field so that our readers can make the transition with little extra work. To begin that process, I propose the simple text A simple logistic function may be defined by the mathematical formula:

--Михал Орела (talk) 07:40, 19 October 2008 (UTC)

Now it is clear that we need to add explanatory information on the fact that the variable P may be read as population and variable t may be read as time. Will do that now.--Михал Орела (talk) 07:47, 19 October 2008 (UTC)

Massaging the math
I am thinking again about the Wikipedia reader who might find the "usual" Mathematicians' favorite form
 * $$P(t) = \frac{1}{1 + e^{-t}} \! $$

a little bit frightening. I am also thinking that a linearized form of the exponential function ought to be included as well:
 * $$P(t) = \frac{1}{1 + exp(-t)} \! $$

and ultimately
 * $$P(t) = ({1 + exp(-t)})^{-1} \! $$

Now the issue is appearance on the page: same line (which I favor) or 3 separate lines (which "waste" space). — Михал Орела (talk) 08:35, 11 September 2009 (UTC)

So! My proposed change is
 * $$P(t) = \frac{1}{1 + e^{-t}} \equiv  \frac{1}{1 + exp(-t)} \equiv ({1 + exp(-t)})^{-1}\! $$

It looks good and gives all the info needed. — Михал Орела (talk) 08:40, 11 September 2009 (UTC)

 * I don't agree. It looks cluttered and does not lead to any information. Anyone who is interested in knowing logistic function would know that "e" and "exp" are the same. Similarly, the differential equation is currently written as:
 * $$\frac{d}{dt}P(t) = P(t)(1-P(t)) \equiv \frac{dP}{dt}=P(1-P) \equiv P' = P(1-P)\!$$

which looks ugly. Why do you want a reader to sift through all the unnecessary equalities. The following is sufficient and complete:
 * $$\frac{d}{dt}P(t) = P(t)(1-P(t)) \!$$

—Preceding unsigned comment added by 65.202.28.10 (talk) 00:11, 23 February 2010 (UTC)

Use of footnotes
I foresee the need to use footnotes to explain certain relationships to other mathematical forms of the same things. Hence I have introduced the appropriate section entitle "Notes".

Logistic differential equation
The next major task is to present the simple differential equation into the wider mathematical context. In other words, from this starting point we ought to generalize and make connection with the original of Pierre François Verhulst. This is the task scheduled for today.--Михал Орела (talk) 08:14, 19 October 2008 (UTC)

I have already introduced a section for footnotes in preparation for the development of the logistic differential equation. It now makes good sense to introduce the logistic differential equation in a section of its own. --Михал Орела (talk) 10:12, 19 October 2008 (UTC)

The first concrete step to take to achieve this goal will be to move the material in the section "In Ecology: modeling population growth" as close as possible to the top of the article. After all, this is where it all began. I will do this now and add in the appropriate Wikipedia reference to Verhulst.--Михал Орела (talk) 14:23, 20 October 2008 (UTC)

To highlight this "ecology section" I have introduced a strong visual marker — the usual Wikipedia Commons image of Verhulst. This will draw the eye to the section and keep the reader on the page. No need to click away to the Verhulst Wikipedia page for the basic information on the original differential equation, which is already here.--Михал Орела (talk) 14:50, 20 October 2008 (UTC)

The next task is to put the following into an appropriate place. "The Verhulst equation, (1), was first published by Pierre F. Verhulst in 1838 after he had read Thomas Malthus' An Essay on the Principle of Population. Verhulst derived his logistic equation to describe the self-limiting growth of a biological population. The equation is also sometimes called the Verhulst-Pearl equation following its rediscovery in 1920. Alfred J. Lotka derived the equation again in 1925, calling it the law of population growth."

It is very good text! But the information needs to be "spread around". It would not suprise me if it is not already on Verhulst's Wikipedia page. We want to keep it here. My proposal is to place it into the footnote section. Notice that the reference number (1) used, no longer applies. —Preceding unsigned comment added by Mihal Orela (talk • contribs) 15:03, 20 October 2008 (UTC)

request
can we please have instructions for how to fit a logistic curve's parameters to data? Is there an analytic way to do this; or do you just have to use numerical methods like gradient descent and pray that it converges?

 * The Levenberg-Marquardt algorithm is a very general method that may be applicable here, depending on what exactly it is that you want to do. --MarkSweep (call me collect) 08:50, 22 March 2006 (UTC)

Plot
The plot needs labels on the X and Y axis! Targa86 21:25, 28 June 2007 (UTC)

A suggestion on the plot: we should have two - one labeled with the terms used in describing the function and the other to serve as an example at specific values (the current one works, but just with the values of L,k and x0 specified). This will greatly aid in comprehending the curve. Viraj Paripatyadar (talk) 07:48, 26 December 2014 (UTC)

wishlist entry
Would be neat to have a 1-2 sentence explanation in laymen's terms what is it good for, and why does it fit better or worse a task than other, comparable things/methods/whatevers. See standard deviation for example, where the section Interpretation and application explains in simple terms what is that good for. (Many statistical terms could use such an "interpretation"... most of them mathematically defines the terms but forget to explain it to shoemakers and milkmen. :-) ) --grin ✎ 07:42, 2004 May 6 (UTC)

I agree. As someone researching the diffusion of innovations, which follows an s-curve, I'd like to know what an s-curve really means. I'm not a shoemaker or milkman, but I would like to have a better understanding of what an s-curve is. --Westendgirl 22:59, 3 Jan 2005 (UTC)

 * This is largely already there; it's just not explicitly labeled as the answer to that question. I'll return to this article soon. Michael Hardy 01:04, 4 Jan 2005 (UTC)

 * It might be there, but I don't have the math background to understand it. :) My husband, a mathematician, assures me that all I need to know (for my purposes) is that an s-curve is a curve shaped like an S, as a result of data that has been plotted. I recognize that I don't need to understand the formula, but is this s-shape all I (and other lay readers) need to know? --Westendgirl 05:37, 4 Jan 2005 (UTC)
 * Done.Ancheta Wis 10:29, 8 Apr 2005 (UTC) Cleanup note removed

 * In effect, the S-curve is the simplest kind of long-term transition you can have where both the starting point and ending point are bounded. The differential equation governing the process is a polynomial of the smallest order (quadratic) that will accomplish the trick. Polynomials of order 0 and 1 won't do the trick.

 * It also occurs naturally in the study of any chemical process where both sides of a reaction, e.g. 2A <-> B+C are of order 2 or less. The resulting differential equation governing the rate is then quadratic and the solution (if bounded) will be a logistic.

 * In the study of the world population curve, contrary to the article's assertion, there actually is a good fit -- provided one takes the lower asymptotic to be non-zero. The underlying equation generalizes the Verhulst equation (also called the Malthus-Verhulst equation) by allowing a zero order term on the right, x' = A + Bx + Cx^2 with non-zero A. In fact, what one finds is that for the 1974-2004 range, there is a near-exact symmetry about 1989 (if I recall, it's P(1989-x)+P(1989+x) = 10.386 billion +/- 5 million, according to the international database of the US Census Bureau) and the curve closely fits a logistic with an upper asymptotic of 7.8 billion. The fit is within 6 million over the entire 1974-2004 range with a root-mean-square deviation of around 3 million!

 * For earler segments of the curve, there is a poor fit to a logistic primarily because (a) there are natural phase boundaries c. 1950 and c. 1850 which are impossible to fit a logistic across, and (b) the 1850-1950 segment does not fit any logistic at all, but rather the limiting case: an exponential with a lower asymptotic of about 1 billion. -- Mark, 26 September 2006

Standard formula needed
The three pages sigmoid, sigmoid function, and logistic curve seemed rather confusing for readers. So I have moved all info on the "standard" logistic curve 1/(1+exp(-t)) to sigmoid function, and kept here only the stuff about more general logistic curves that are shifted and scaled copied of the latter. I have provided a general formula for these curves, but I am not familiar with this field so I do not know whether the formula and parameters that I picked are OK. If there is a "canonical" formula, would someone please provide it? Also the plot shows the standard sigmoid function; here one should have a plot of the more general logistic curve, shifted and scaled. Jorge Stolfi 07:37, 2 Jul 2004 (UTC)

It is still confusing that there are two different formulas presented right at the top of the article. They are the same, but one is forced to do a little bit of algebra to see that is the case, and I don't see why there needs to be a change in notation, nor the difference between the "logistic function" and the "logistic sigmoid function". —Preceding unsigned comment added by Aheilbut (talk • contribs) 01:59, 7 August 2008 (UTC)

I am proposing to replace the "two different formulas" with one and to show how the two are related by integration of logistic differential equation.--Михал Орела (talk) 19:48, 17 October 2008 (UTC)

Logistic curve vs. logistic function
Argh.. I moved logistic curve to logistic function because it seemed more logical, but now I see that most users call it "curve". Profuse apologies. If you can, could you please reverse the move, making logistic function into a redirect? Thanks... Jorge Stolfi 08:01, 2 Jul 2004 (UTC)

Typo
I think there is a mistake in the line: "In 1924 during The Great Depression Professor Ray Pearl and Lowell J. Reed used Verhulst's model to predict an upper limit of 2 billion for the world population. This was passed in 1930..." The Roaring 20s were at their height in 1924. Black Tuesday wasn't until 1929.

Article has wrong focus
The phrasing and structure of the article mistakes the logistic function for one of its applications, namely modeling population growth. Instead, the logistic function should be introduced as a mathematical function. It surely it has mathematical properties. Other important applications are found, for example, in machine learning and statistics. -Pgan002 21:47, 7 February 2006 (UTC)

Another form of the logistic function
I've only taken one year of calculus, but we learned the logistic function as $$P(t) = {M \over {Ae^{-kt} + 1}} $$, not :$$P(t) = a\frac{1 + m e^{-t/\tau}}{1 + n e^{-t/\tau}} \!$$. Can someone explain the differences to me? If possible, I'd like to incorporate the derivation of the logistics formula that I added [|here] into this page. --Alex S

 * Your formula is a special case of the presented formula with $$a=M, m=0, n=A, \tau=k^{-1}$$

MisterSheik 15:19, 26 June 2006 (UTC)
 * It's only the same curve moved by translation : $$P(t) = am/n + a(1-m/n)\frac{1}{1+ne^{-t/\tau}} = am/n + \frac{M}{1+Ae^{-kt}}$$. It's not an usual presentation but why not. My english is too bad. Sorry, I'm french - HB - 2 August 2007

Another pov
I came across this curve while examining the qustion: what does it mean to double a probability? Eventually I decided that a nice way to do it is to duble the ratio r = p/(1-p). In effect, this treats the probability as being expressed as gambling odds.

If you take the log of this value ln(p/(1-p)) and flip the x any y axes y=exp(x)/exp(x+1) you get the logistical curve. Pmurray bigpond.com 06:08, 5 June 2006 (UTC)

proposed merge with logit
The page on logit and logistic function appear to regard the exact same topic, the logistic function. As such, I propose that they be merged. The primary portion of the logit page that I think bears inclusion in this page is the comment at the top regarding logistic regression (in italics). Pdbailey 17:11, 13 June 2007 (UTC)
 * I am not against a merge, but let's note they are different topics, albeit each other's inverse. Logit would need its own section which would be a redirect target, right?  Now that the logit page is cleaned up, it may be doable.  Baccyak4H (Yak!) 17:37, 13 June 2007 (UTC)

 * The more I thought about it, these two articles focus quite clearly on the two functions and little ink (pixels?) would be spared merging. The fact that one is the others inverse doesn't appear to be relevant to either article's point. Pdbailey 23:45, 13 June 2007 (UTC)

no equation 1
The section on history suggests that equation 1 was first proposed by... but there is no equation 1. I'd link it if I knew which one it was. Pdbailey 17:09, 13 June 2007 (UTC)

Logistic sigmoid function
The following text is incomplete because it does not give the original equation in which the parameters a, m, n, and τ occur. “The sigmoid function with a = 1, m = 0, n = 1, τ = 1, namely

 * $$P(t) = \frac{1}{1 + e^{-t}}\!$$

is called the logistic sigmoid function or sometimes the standard sigmoid curve.”

I propose to correct this as soon as possible.--Михал Орела (talk) 15:06, 17 October 2008 (UTC)

[1] The first task is to merge the two variants of the "definition" of the function:

"A logistic function is defined by the mathematical formula:

 * $$Z(\theta) = \frac{e^{\theta}}{1 + e^{\theta}} \! $$

..." and "The sigmoid function with a = 1, m = 0, n = 1, τ = 1, namely

 * $$P(t) = \frac{1}{1 + e^{-t}}\!$$

..."

Given that the function variable name $$P$$ is used consistently in most of the article, it seems to make good sense to keep it. --Михал Орела (talk) 18:07, 17 October 2008 (UTC)

[2] Before doing the merge it is a good idea to harmonize with what already exists in Wikipedia. For example, in Logistic regression the definition is given as "...
 * $$f(z)=\frac{1}{1+e^{-z}}$$

..." My suggestion will be to keep the function variable name $$P$$ with parameter $$t$$.--Михал Орела (talk) 18:19, 17 October 2008 (UTC)

[3] If we look at the given logistic differential equation "...
 * $$\frac{dP}{dt}=P(1-P), \quad\mbox{(2)}\!$$

..." we readily find the (symbolic) solution (using Mathematica, for example) to be
 * $$P(t)=\frac{e^{t}}{e^{t}-e^{c}}$$

Choosing the constant of integration $$e^{c}=-1$$ gives the desired result: the original first definition of the logistic function with $$P$$ ==> $$Z$$ and $$t$$ ==> $$\theta$$.--Михал Орела (talk) 19:08, 17 October 2008 (UTC)

Here is the proposed solution for the article:

A logistic function or logistic curve is the most common sigmoid curve. It models the S-curve of growth of some set P. The initial stage of growth is approximately exponential; then, as saturation begins, the growth slows, and at maturity, growth stops.

A logistic function is defined by the mathematical formula:

 * $$P(t) = \frac{1}{1 + e^{-t}} \! $$

The logistic function finds applications in a range of fields, including artificial neural networks, biology, biomathematics, economics, chemistry, mathematical psychology, probability and statistics.

The logistic function is the solution of the first-order non-linear differential equation

 * $$\frac{dP}{dt}=P(1-P) \!$$

with boundary condition P(0) = 1/2. This equation is the continuous version of the logistic map. One may readily find the (symbolic) solution (using Mathematica, for example) to be
 * $$P(t)=\frac{e^{t}}{e^{t}-e^{c}}$$

Choosing the constant of integration $$e^{c}=-1$$ gives the other well-known form of the definition of the logistic curve
 * $$P(t) = \frac{e^{t}}{1 + e^{t}} \! $$

The logistic curve shows early exponential growth for negative t, which slows to linear growth of slope 1/4 near t = 0, then approaches y = 1 with an exponentially decaying gap.

The logistic function is the inverse of the natural logit function and so can be used to convert the logarithm of odds into a probability; the conversion from the log-likelihood ratio of two alternatives also takes the form of a logistic curve.

The logistic sigmoid function is related to the hyperbolic tangent, A.p. by
 * $$2 \, P(t) = 1 + \tanh \left( \frac{t}{2} \right).$$

I propose to post this within 24 hours if there are no major objections. It is still not exact. For example, I still need to state that $$t$$ ranges over the Real numbers from $$-\infty$$ to $$+\infty$$. --Михал Орела (talk) 19:45, 17 October 2008 (UTC)

Added internal link to Mathematica--Михал Орела (talk) 04:47, 18 October 2008 (UTC)

The new restructured text has now been posted. I will add some minor additions later.--Михал Орела (talk) 05:09, 19 October 2008 (UTC)

Massaging the math
The original definition has now been expanded to read
 * $$P(t) = \frac{1}{1 + e^{-t}} \equiv  \frac{1}{1 + exp(-t)} \equiv ({1 + exp(-t)})^{-1}\! $$

For the purposes of consistency it is necessary to do a little rewriting for the corresponding differential equation
 * $$\frac{dP}{dt}=P(1-P) \!$$

and its solution
 * $$P(t)=\frac{e^{t}}{e^{t}-e^{c}}$$

which is also written as
 * $$P(t) = \frac{e^{t}}{1 + e^{t}} \! $$

This needs to be done carefully. I will post the suggested rewrite here first. — Михал Орела (talk) 08:56, 11 September 2009 (UTC)

For the differential equation I have now included
 * $$\frac{d}{dt}P(t) = P(t)(1-P(t)) \equiv \frac{dP}{dt}=P(1-P) \equiv P' = P(1-P)\!$$

to replace the original equation
 * $$\frac{dP}{dt}=P(1-P) \!$$

My reasoning is this. Those who are not already familiar with all the conventions of the mathematics of differential equations may need to see (and learn) about the notations used. I still need to mention the "dot" notation which is still in common usage for differentiation with respect to time. — Михал Орела (talk) 08:40, 12 September 2009 (UTC)

image problem
The first image on the page, the plot of the logistic function, appears to be broken to me. Anyone else having this problem? 128.97.68.15 (talk) 17:18, 30 October 2008 (UTC)

 * At first glance it looks OK to me - a red S-shaped curve passing through (0, 0.5) with asymptotes y=0 and y=1. I'm using IE6. What do you see?--A bit iffy (talk) 17:26, 30 October 2008 (UTC)

 * It looks fine on Firefox and Safari; I will check with Opera now. --Михал Орела (talk) 09:08, 31 October 2008 (UTC)

 * Just checked with Opera browser; everything is "beautiful" --Михал Орела (talk) 09:16, 31 October 2008 (UTC)

Solution of the Logistic Differential Equation
Can we say more about the solution to the logistic differential equation than to use Mathematica? The equation is a lovely example of a Bernoulli differential equation, and mentioning the fact gives an easy explicit solution given an initial value. No need to mask pretty mathematics. --Moly 04:24, 21 January 2009 (UTC) —Preceding unsigned comment added by Moly (talk • contribs)

 * Looked at the Bernoulli differential equation you mentioned! It is very raw Mathematics :-) In other words there is very little "English text" to suggest to the "uninitiated" where the equation comes from and why it is significant. Perhaps you might elaborate on its "beauty" there and then see how to fit the logistic differential equation example into place?--Михал Орела (talk) 14:17, 27 January 2009 (UTC)

Neural Networks
I am looking at the following section: "Logistic functions are often used in neural networks to introduce nonlinearity in the model and/or to clamp signals to within a specified range. A popular neural net element computes a linear combination of its input signals, and applies a bounded logistic function to the result; this model can be seen as a "smoothed" variant of the classical threshold neuron.

A reason for its popularity in neural networks is because the logistic function satisfies the differential equation

 * $$y' = y(1-y).\,$$

The right hand side is a low-degree polynomial. Furthermore, the polynomial has factors y and 1 − y, both of which are simple to compute. Given y = sig(t) at a particular t, the derivative of the logistic function at that t can be obtained by multiplying the two factors together. These relationships result in simplified implementations of artificial neural networks with artificial neurons."

There are no citations to support the assertions in the text. I will look into remedying this now. In addition, to argue the case that it is popular in neural networks precisely because it satisfies the given differential equation is not a good argument, in my opinion. I will replace this with specific examples from the neural network literature (and thus "prove" the assertion by example :) )--Михал Орела (talk) 16:46, 29 January 2009 (UTC)

I propose to replace the text "A reason for its popularity ... artificial neural networks with artificial neurons" with the following: A common choice for the activation or "squashing" functions, used to clip for large magnitudes to keep the response of the neural network bounded is

 * $$g(h) = \frac{1}{1 + e^{-2 \beta h}} \! $$

which we recognize to be of the form of the logistic function.

The text is taken from Gershenfeld 1999, p.150--Михал Орела (talk) 19:05, 29 January 2009 (UTC)

Why is it called "logistic"?
The origin of the term "logistic" is obscure. This word is far from self-explanatory. Thus, unlike for most other scientific terms, trying to look at its latin/greek etymology (e.g. consulting wiktionary) provides no insight really to the meaning of the concept. Could someone throw some light on the logic (if any) behind the word "logistic", especially when used in the present context? Typofier 22:34, 13 February 2009 (UTC) —Preceding unsigned comment added by Typofier (talk • contribs)

It's worse than you think, Verhulst gave it the name logistic with no justification at all :

"Nous donnerons le nom de logistique à la courbe caractérisée par l'equation précédente."

That's it. Until then the word logistique was associated with military operations, so it seems it could have been called verhulstian curve as well.Lbertolotti (talk) 14:29, 19 October 2014 (UTC)

Thank you Lbertolotti very much for the exhaustive − albeit unfortunate − explanation! In my opinion this etymological anecdote should cleary be added to the Article. It also serves as a great (sad) example of how unsystematic even prominent scientists may be in their use of terminology. Typofier 04:45, 8 January 2015 (UTC) — Preceding unsigned comment added by Typofier (talk • contribs)

Logistic function and chaos.
I miss some information about this... --Andrestand (talk) 10:26, 24 August 2009 (UTC)

You will find this information at Logistic map. — Михал Орела (talk) 08:23, 10 September 2009 (UTC)
 * So the recurrence version is chaotic, the continuous version is not chaotic? --Alex1011 (talk) 10:18, 12 May 2012 (UTC)

Logistic function and heartbreak
Using the right variables, the population function can help you determine how long it takes to heal a broken heart:

 * $$ t = \frac{.02 e^{.1x}}{2 + .01 \left( e^{.1x} - 1\right)} $$

where x is the time you were with someone in months, and t is the expected grieving time in months. Alternately, you might try seeing a counselor.

Loosenut (talk) 04:41, 23 March 2010 (UTC)

Expand chemistry
Besides autocatalytic, two other items that are related: 1) (pH) titration curves, and 2) Avrami equation for crystallization. Dagordon01 (talk) 01:38, 6 June 2011 (UTC)

If you present a formula, define it's terms. All of them.
What is "d"? How am I supposed to find out? If you assume the reader already knows, what is the purpose of Wikipedia? DEFINE TERMS. PROVIDE LINKS. TEACH. Thanks. — Preceding unsigned comment added by 70.41.216.250 (talk) 19:43, 12 March 2012 (UTC)

 * In:       $$\frac{d}{dt}P(t) $$,

$$\frac{d}{dt}$$ is a differential operator. It is calling for the derivative of $$P(t)$$ with respect to $$t$$.Phmoreno (talk) 23:49, 12 March 2012 (UTC)

relating similarities to the error function
I'm really a layman but i can't help but notice similarities to the error function, could someone explain whether and if so what the similarities are between this two? thanks in advance Andy Jiang (talk) 05:27, 17 May 2012 (UTC)

Is there one logistic function or many?
In the beginning of the article, one reads: The logistic function is the sigmoid curve with equation: $$f(x) = \frac{1}{1 + \mathrm e^{-x}} $$. But later on, the plural logistic functions is also used. Is there one logistic function or are there many? Jaan Vajakas (talk) 14:55, 9 February 2014 (UTC)

Congruency between Sigmoid Function and Logistic Function
Currently, the intro of this page reads "A logistic function or logistic curve is a common special case of the more general sigmoid function," and the intro to the sigmoid function on its page reads "Often, sigmoid function refers to the special case of the logistic function." They cannot be special cases of each other. Also, they are both defined exactly the same, which doesn't make sense. If that is true, then they are equivalent and I would think the two pages should be merged or link to each other. Is it correct that the sigmoid function is a special case of the "logistic curve"? 2001:4898:80E0:EE43:0:0:0:3 (talk) 18:41, 7 August 2014 (UTC)

Constructal theory link
I'm not very proficient in editing wikipedia, so hopefully someone else can look into this and figure out the right course of action. In "See Also", there is a link to "Constructal Law" which I believe bears little relation to the topic of this page. The link was put there by a user "Mre env" (http://en.wikipedia.org/wiki/User:Mre_env) whose edit history seems to be entirely based upon spreading links and references to this supposed law around the wiki. I've undone two of his recent edits, which even plagiarized the source he was citing, but I imagine there are better ways to handle this, since it seems to be continuous and pervasive. 38.65.195.5 (talk) 00:07, 19 February 2014 (UTC)
 * I've made a notice on Fringe theories/Noticeboard, so hopefully this will get figured out. 38.65.195.5 (talk) 00:58, 19 February 2014 (UTC)
 * It seems to be a small consensus that it is a WP:FRINGE topic, and it is also referenced in the section "In design in nature: spreading and collecting flows". I'm removing both the link and that section. 38.65.195.5 (talk) 18:28, 19 February 2014 (UTC)

Is it a logistic function or the logistic function?
According to the first sentence in the article, it is a logistic function, indicating that there is a family of logistic functions. At the same time, it defines such a function as

 * $$f(x) = \frac{1}{1 + \mathrm e^{-x}},$$

indicating that there is only one such function. So, is there many logistic functions or only one? —Kri (talk) 20:43, 22 October 2014 (UTC)

 * If one reads the article carefully, the function you mention above is a standard logistic function. The usual parameterized version of the logistic function is noted in the lead. Also there is no mention of a family of logistic functions; rather it is a logistic family of distributions, which is a different thing. I have also seen mentioned a family of logistic functions, in the context of iterated functions and period doubling in the logistic map. --Mark viking (talk) 19:12, 8 April 2016 (UTC)

Logistic differential equation - simpler language
In the section "Logistic differential equation", we have three ways of expressing zero: "0", "zero" and "null"; and two ways of expressing one: "1" and (strangely) "unit". I'm going to simplify these to use the figures "0" and "1", or the words "zero" and "one", as appropriate. yoyo (talk) 16:15, 9 October 2017 (UTC)

 * Done. Turns out it was clearer to use the figures "0" and "1" rather than the words "zero" and "one" in those places.  yoyo (talk) 16:25, 9 October 2017 (UTC)

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title: Talk:Logistic function


text:
List of mine countermeasure vessels of the Royal Navy

Active ships

 * Hunt-class mine countermeasures vessels
 * HMS Ledbury (M30)
 * HMS Cattistock (M31)
 * HMS Brocklesby (M33)
 * HMS Middleton (M34)
 * HMS Chiddingfold (M37)
 * HMS Hurworth (M39)
 * Sandown-class minehunters
 * HMS Penzance (M106)
 * HMS Pembroke (M107)
 * HMS Bangor (M109)

Historical ships
Naval mine clearance was originally done by whatever type of vessel could easily be adapted to the task, paddle steamers proving particularly suited due to their shallow draught. In both World Wars naval trawlers were used, as they were naturally suitable for wire sweeping. In World War II this task was given to smaller trawlers of about 300 tons, larger ones being used for anti-submarine work. The increased sophistication and threat posed by the mine meant that specialist mine countermeasure vessels eventually had to be built: the Minesweeping Sloop. This term was officially dropped in 1937, but remained in use nonetheless. The Royal Navy has possessed such vessels since 1914.

There were also some conversions of ships originally built for other purposes for special minesweeping. This was mainly early in World War II for sweeping acoustic and magnetic mines, and later in the war for sweeping influence mines. The ships selected were of varying origin and age and thus do not form a class as such.

 * Flower-class sloop sloop (112 ships in 4 sub-classes, launched 1914–1918) convoy sloops intended originally for minesweeping
 * Hunt class, Belvoir group (20 ships, launched 1916–17) Ailsa twin-screw coastal minesweeping sloops
 * Hunt class, Aberdare group (87 ships, launched 1917–1919) Admiralty twin-screw coastal minesweeping sloops
 * Dance-class minesweeper (14 ships, launched 1917–1919) tunnel-screw coastal minesweeping sloops
 * Racecourse-class minesweeper (32 ships in 2 sub-classes, launched 1916–1918) paddlewheel coastal minesweeping sloops
 * Halcyon-class minesweeper (7 reciprocating and 14 turbine ships, launched 1933–1939) twin-screw minesweeping sloops
 * Bangor-class minesweeper (14 ships, launched 1940–1942) diesel twin-screw single-role minesweeping sloops
 * Blyth class (Bangor class II) (19 ships, launched 1940–1943) reciprocating Bangor variant
 * Ardrossan class (Bangor class III) (26 ships, launched 1940–1942) turbine Bangor variant
 * Bathurst-class corvette (47 ships, launched 1940–1943 only served with the Royal Australian Navy and Royal Indian Navy) Australian Bangor variant
 * MMS-class minesweeper (403 ships, launched 1940–1945) inshore acoustic / magnetic motor minesweepers
 * Algerine-class minesweeper (98 ships, launched 1941–1945) twin-screw multi-role minesweeping sloops
 * Catherine-class minesweeper (22 ships, twin-screw multi-role minesweeping sloops, transferred from the US Navy in 1941 under the Lend-Lease program)
 * BYMS-class minesweeper (150 ships, launched 1941–1943) British-built acoustic / magnetic motor minesweepers
 * Cybele-class mine destructor vessel (2 ships, launched 1943) towed pressure-mine detonating vessels
 * Ton-class minesweeper (116 ships, launched 1952–1959) open-water minesweepers, minehunters and mine countermeasures vessels
 * Ham-class minesweeper (93 ships, launched 1954–1959) inshore minesweepers
 * Ley-class minehunter (10 ships, launched 1952–1955) inshore minehunters
 * Wilton-class minesweeper/minehunter (1 ship, launched 18 January 1972) open-water minesweeper and minehunter. Prototype ship built of glass reinforced plastic (GRP) to same hull design as Ton class. Forerunner of the Hunt and Sandown classes, also built of GRP.
 * Hunt-class mine countermeasures vessel (13 ships, launched 1978–1988) mine countermeasures vessels
 * Venturer-class minesweeper (2 ships, bought 1979) deep-water single-role minesweepers
 * River-class minesweeper (12 ships, launched 1982–1985) deep-water single-role minesweepers
 * Sandown-class minehunter (12 ships, launched 1990–2001) single-role minehunters

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


text:
List of survey vessels of the Royal Navy

Antarctic patrol vessel

 * HMS Protector (A173) (2011–) which carries the survey motor boat (SMB) James Caird IV.

Ocean survey vessels

 * HMS Scott (H131) (1997–)

Coastal survey vessels

 * Survey Motor Launch
 * HMS Magpie (H130) (2018–)

Antarctic patrol vessels

 * HMS Protector (A146) (1955–70)
 * HMS Endurance (1967) (1968–91)
 * HMS Endurance (A171) (1991–2008)

Ocean survey vessels

 * Hecla-class survey vessel
 * HMS Hecla (A133) (1964–97)
 * HMS Hecate (A137) (1965–90)
 * HMS Hydra (A144) (1966–86)
 * HMS Herald (H138) (1974–2001)

Coastal survey vessels

 * Bulldog-class survey vessel
 * HMS Beagle (A319) (1968–2002)
 * HMS Bulldog (A317) (1968–2001)
 * HMS Fawn (A325) (1968–91)
 * HMS Fox (A320) (1968–89)
 * HMS Roebuck (H130) (1986–2010)
 * Echo-class multi–purpose survey vessels
 * HMS Echo (H87) (2003–2022) which carries SMB Sapphire.
 * HMS Enterprise (H88) (2003–2023) which carries SMB Spitfire.

Inshore survey vessels

 * Echo-class survey ship (1957)
 * HMS Echo (A70) (1958–85)
 * HMS Egeria (A72) (1959–85)
 * HMS Enterprise (A71) (1959–85)
 * Ham-class minesweeper
 * HMS Waterwitch (ex–HMS Powderham) (1964–86)
 * HMS Woodlark (ex–HMS Yaxham) (1964–86)
 * Ton-class minesweeper
 * HMS Mermaid (ex–HMS Sullington) (1964–68)
 * HMS Myrmidon (ex–HMS Edderton) (1964–68)

Survey Motor Launches (SML)

 * SML 2
 * SML 4
 * SML 6
 * SML 322
 * SML 323
 * SML 324
 * SML 325
 * SML 326
 * HMS Meda (1943) (ex–HDML 1301) (1945–1966)
 * HMS Medusa (A353) (ex–HDML 1387) (1952–1965)
 * HMS Gleaner (H86) (1983–2018)

Earlier survey vessels

 * HMS Merlin (1666) (1666–1698), the Navy's first hydrographic survey vessel
 * HMS Hecate (1839) (1839–65)
 * HMS Myrmidon (1867) (1867–88)
 * HMS Triton (1882)
 * HMS Fantome (1901) (1906–14, 1920–24)
 * HMS Endeavour (1912) (1913–42)
 * HMS Melisande (1918–19)
 * HMS Challenger (1931) (1932–53)
 * HMS White Bear (1939–45)
 * HMS Vidal (1954–71)
 * Hunt-class minesweeper (1916)
 * HMS Beaufort (1919) (1920–35)
 * HMS Fitzroy (1920–38)
 * HMS Flinders (1920–38)
 * HMS Kellett (1920–38)
 * 24-class sloop
 * HMS Iroquois (1918) (1923–31)
 * HMS Herald (ex–HMS Merry Hampton) (1924–39)
 * HMS Ormonde (1918) (1924–36)
 * Bittern-class sloop
 * HMS Stork (L81) (1936–39)
 * Hastings-class sloop
 * HMS Folkestone (L22) (1938)
 * HMS Scarborough (L25) (1938)
 * Halcyon-class minesweeper
 * HMS Franklin (J84) (1938–52)
 * HMS Gleaner (J83) (1938–39)
 * HMS Jason (J99) (1938–39)
 * HMS Scott (J79) (1939–64)
 * HMS Seagull (J85) (1946–50)
 * HMS Sharpshooter (J68) (1946–62) – renamed HMS Shackleton, 1955
 * Bay-class frigate
 * HMS Dampier (K611) (1948–68)
 * HMS Owen (K640) (1949–65)
 * HMS Cook (K638) (1950–64)
 * HMS Dalrymple (K427) (1950–66)


text:
Talk:Katy Rose

Image
could one upload a picture of her according to fair use policy?Plato 07:51, 6 May 2004 (UTC)
 * No, according to Non-free content it is not acceptable to use a non-free image where it could reasonably be replaced by a free one.-- Beloved Freak  13:26, 10 February 2008 (UTC)

Official Website
What happened to it? When you click on a link or type in the address, it redirects you to V2 music. —Preceding unsigned comment added by 65.191.82.234 (talk • contribs) 20:56, 4 June 2007

Unsourced material
I have removed some statements relating to anorexia, suicidal thoughts and drug use because I can't find any reliable sources to back them up. They really need sources before being added back.-- Beloved Freak  13:26, 10 February 2008 (UTC) Actually, on Katys myspace page, she herself talks about her past. She mentions being sexually abused, drug abuse and an ongoing struggle with anorexia. Check out her blog. —Preceding unsigned comment added by 24.65.199.200 (talk) 07:46, 17 September 2008 (UTC)

External links modified
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title: Talk:Katy Rose


text: User talk:152.118.24.3

title: User talk:152.118.24.3


text:
Yacas

Yacas is a general-purpose computer algebra system. The name is an acronym for Yet Another Computer Algebra System.

Released under the GNU Lesser General Public License, Yacas is free software.

YACAS is a program for symbolic manipulation of mathematical expressions. It uses its own programming language designed for symbolic as well as arbitrary-precision numerical computations. The system has a library of scripts that implement many of the symbolic algebra operations; new algorithms can be easily added to the library. YACAS comes with extensive documentation covering the scripting language, the functionality that is already implemented in the system, and the algorithms used. Its development started in early 1999.

Yacas handles input and output in plain ASCII or in OpenMath, either interactively or in batch mode.

title: Yacas


text:
Talk:List of Hungarian writers

Untitled
This list have to be cross-checked by google/searching, because in wikipedia some names are written without accents, some with incorrect accents (Dezsö instead of Dezső, etc), and some proper ones. I fixed the most obvious ones only. --grin ✎ 08:03, 2004 May 6 (UTC)

 * I'm not sure English Wiki can handle the letter "ő". When I was writing an article about Győr someone moved it to Györ. Alensha 10:58, 19 Oct 2004 (UTC)

 * I was recently told on the talk page of Győr that the letter ő doesn't cause problems in the text, but shoudn't be in the title of the article. In this article I'll keep the links to appear as Dezső for example, but it will lead to an article with Dezsö in its title. Alensha 11:18, 23 Oct 2004 (UTC)

About a month ago all Hungarian-related titles in the English Wikipedia which should originally contain the letters "ő" and "ű" (and which contained the letters "ö" and "ü" instead), including people's and cities'/town's names, were moved to versions containing "o" and "u" respectively. For example the article "Sándor Petöfi" was moved to "Sándor Petofi". Soon templates were added (named "titlelacksdiacritics", formerly "wrongtitle") into the articles, notifying users that these are meant as containing "ő" and "ű". It seems that replacing "ő" and "ű" with "ö" and "ü", however logical it may seem to us, Hungarians, is not a practice supported by speakers of English, and no other "approaching" characters are used in other Wikipedias, either. This means that (according to the now-common Wikipedia usage concerning Hungarian names) no substituting "ö"s and "ü"s should be used in Hungarian names, because:
 * in article texts, the original "ő" and "ű" should be retained,
 * in article titles, they should be replaced by "o" and "u".

Example: the title will be "Sándor Petofi", and his article should be linked as Sándor Petőfi. This is the general usage I commonly encountered in the English Wikipedia in the last half a year, which I can suggest too (until the problem of "ő" and "ű" is finally solved).

Adam78 17:09, 19 Jun 2005 (UTC)

I know, it was an old discussion, I just corrected a typo in it :) (still dislike this rule of substituting ő with o though; I hope they solve this problem soon.) Alensha 20:42, 19 Jun 2005 (UTC)

title: Talk:List of Hungarian writers