Talk:Hyperbolic function

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[edit] Maclaurin not Taylor

The series presented here are Maclaurin series, not Taylor series. We should either add in an "a" term - the taylor series about "a", or call them Maclaurin series. Gareth 139.80.48.19 21:00, 14 November 2007 (UTC)

[edit] ???

well, ppl look for this page are generally for a glance of the meaning of cosh. wth u described so many complicated information (not professional tho) but not instead just fukcing tell me how to type cosh in a standard calculator?? —Preceding unsigned comment added by 203.122.102.163 (talk) 02:06, August 29, 2007 (UTC)

its there. twice. in big print.

[edit] Error in the LaTeX and normal images

I can't see them, look at the error: Failed to parse (Can't write to or create math output directory): \sinh(x) = \frac{e^x - e^{-x}}{2} = -i \sin(i x) Why is this?

I found something similar, not with this equation, but with \sech . I added braces around ix to get \sec {ix} and that seemed to work. What is strange is that all of the other functions with the same format work well for me.

Garethvaughan 19 Jul 2007 (GMT+12)

[edit] Origin of pronunciations

Does anyone know how the pronunciations for sinh, cosh, etc came about? Do they differ between British and American usages? 128.12.20.195 05:47, 22 January 2006 (UTC)

[edit] ERROR in formula

There is a problem with the expansion series for arccosh. There is a switch of sign in the sum (right), but not in the examples of the first terms (left), and the values do not match. I don't know which is correct.

[edit] Suggestion

Why are you using sinh^2 x for (sinh x)^2?? Go to the inverse function article and it says the definition for f^2 x when not in trigonometry. Then, it has the exception and it says trigonometric functions, not hyperbolic functions. 66.245.25.240 15:42, 12 Apr 2004 (UTC)

By convention this form is used with hyperbolic functions as well. -- Decumanus | Talk 15:43, 12 Apr 2004 (UTC)

The parenthetical comments about pronounciation could be clearer... what type of ch sound in sech, for example

[edit] Some suggestions

What about changing the definition of arccsch(x) to ln(1/x + sqrt(1+x^2)/abs(x))?

Also, why does the definition of arcsech(x) contains the plusminus sign? As far as I know, the definition of arcsech(x) is "the inverse of (sech(x) restricted to [0,+inf))" (Howard Anton et.al., Calculus 7th ed, Chapter 7). In that case we should replace plusminus with plus.

user:Agro_r 11 Feb 2005 (GMT+7)

Definitions can be different. In order to find an inverse function of a many-to-one function, you need to restrict the interval in which the values of the input are defined in order to turn it into a one-to-one function (since a function has to be one-to-many or one-to-one by definition). You can use different values of the interval in order to turn it into a one-to-one function. For example, with cos, you could use [0,pi) or [-pi/2,pi/2). They're both right, I assume. Deskana (talk) 19:21, 8 February 2006 (UTC)

[edit] I need help!

I want know aplications, can somebody help me?

If you are in a spaceship (with no gravity), and want to pretend you are on earth, you can take a piece of string, shape it like the cosh function and take a picture. Then people will think that you are affected by gravity, since a piece of string hanging freely looks like the cosh function. Don't know if they have other uses, I'll leave that to other people who know more, to answer. Κσυπ Cyp 2004年10月27日 (水) 19:56 (UTC)

sinh and cosh are used heavily in electromagnetics applications, as they appear in solutions of Laplace's equation in Cartesian coordinates.

These functions are used heavily in heat transfer, and as general solutions to differential equations eg: θ"+α*θ=0 has a general solution of θ=C1*Cosh(α*x)+C2*Sinh(α*x) (assuming θ is a function of x).

[edit] I have this problem

As can be seen from plots the -cosh(x) function is concave in x.

So, if we have w positive then exp{-wcosh(x)} should alos be convex in x, right? Apparantly not always ... according to this article I have this is only valid iff w{sinh(x)}^2<cosh(x), does anybody see why??

[edit] Arc{hyperbolic function} is a misnomer

Arc{hyperbolic function} is a misnomer

The article states correctly that the parameter t represents an area, rather than a (circular) angle. Note also that t does not represent an arc length. As such, it is actually a misnomer to refer to the inverse hyperbolic functions using the prefix "arc".

OTOH, for the inverses of the trigonometric functions, the prefix "arc" is not a misnomer, since their values may indeed be thought of as representing arc lengths (or circular angles).

Arc{hyperbolic function} probably originated due to a false analogy with trigonometric functions. In any event, it is sometimes used nowadays. But IMO its usage should be deprecated in favor of one of several better alternatives. I prefer the simplest alternative: a{hyperbolic function}, in which "a" may correctly be taken to represent "area".

What do other people think? Should we change the article's currect arc{hyperbolic function} notation to my preference, or some other alternative, or leave the current notation as is?

--David W. Cantrell 07:23, 31 Dec 2004 (UTC)

Hi, I think it the prefix for inverse hyperbolic functions used to be Sect, as in "sector". Why exactly I'm not sure, but that's what I grew up with. Orzetto 09:14, 16 Mar 2005 (UTC)

Probably because sect was easily confused with sec as in secant. Especially if the angle was t, e.g. sectsint would be very ambiguous. 218.102.221.84 07:04, 30 December 2005 (UTC)

The prefix for inverse hyperbolic functions is ar. The original latin names are area sinus hyperbolicus, area cosinus hyperbolicus and the respective functions are named arsinh, arcosh etc. In the US, this knowledge seems to have been lost, so I'm not sure what we should opt for. --Tob 08:39, 7 December 2005 (UTC)

The prefix should be ar not arc for hyperbolic functions. My opinion is that arcsinh ect. is wrong and misleading. SKvalen 18:41, 11 December 2005 (UTC)

It is wrong, but in the US they all use arc. 218.102.221.84 07:04, 30 December 2005 (UTC)

asinh etc. is computer science use and there seems to be a consensus that arc is wrong. Changing to ar. --Tob 14:00, 4 January 2006 (UTC)

An old (American) calculus textbook (Spivak's) has the following to say: "The functions sinh and tanh are one-one; their inverses, denoted by arg sinh and arg tanh (the "argument" of the hyperbolic sine and tangent) ... If cosh is restricted to [0,∞), it has an inverse, denoted by arg cosh...". This seems to confuse the matter further, and a brief Google search suggests that hardly anyone uses this, at least, not on the Internet. 82.12.108.243 15:05, 13 February 2007 (UTC)

[edit] Use of exponents on function names

Hi, I have seen that there is some use of the notation $c o s h 2 ()$ to indicate $c o s h (c o s h ())$ . This should not be done as in some countries $c o s h 2 ()$ actually means $[c o s h ()] 2$ , and this may be a source of confusion. It's evil. Orzetto 09:14, 16 Mar 2005 (UTC)

Is this actually true of non-kiddie level math in those countries: Function composition TomJF 04:09, 12 April 2006 (UTC)

[edit] No Period?

"However, the hyperbolic functions are not periodic." I'm not really an expert in this, but someone told me that the hyperbolic functions do have a period, but it is imaginary. Is this true? --Dragglebaggle 03:09, 20 September 2005 (UTC)

Yes, 2πi. --Macrakis 15:52, 20 September 2005 (UTC)

[edit] ArcTanh(adj,opp)

I needed a hyperbolic analogue of ArcTan[adjacent,opposite], and "Klueless" provided a relationship that I coded as arcTanh[a_,0]:=If[a==0,∞,0,0]; arcTanh[a_,o_]:=If[Chop[a^2-o^2]==0,∞,Log[(a+o)/SQRT[a^2-o^2]] in Mathematica (ref). (The formula is not in the Mathematica functions library) This allowed me to show that, in the algebra with the Klein 4-group as multiplication table, there is a hyperbolic dual of the Argand diagram, with {a,o} <=> {u=Sqrt[a^2-o^2],theta=arcTanh[a,o]} in which "ulnae" (u) multiply and hyperbolic angles (theta) add on multiplication. The hyperbolic plane is covered by two pairs of hyperbolae. Would a referenced write-up of this be acceptable? It seems to be a significant generalization of hyperbolic functions.

(ref) http://library.wolfram.com/infocenter/MathSource/4894

Roger Beresford. 195.92.168.164 08:22, 7 October 2005 (UTC)

Good stuff, but my impression is that Wikipedia should concentrate on widely accepted definitions, not novel insights. By the way, your formulae might be clearer if you didn't use "o" as a variable name and if you didn't you Mathematica-specific conventions -- I assume that If[a==0,∞,0,0] means "if a==0 then ∞ else 0", but I don't understand why there are two 0's there. --Macrakis 15:10, 8 October 2005 (UTC)

ArcTanh[y,x] is not original research, but plagiarism! (I copied from only one source.) ArcTan[y,x] is accepted as it is needed to cope with different angles in opposing quadrants. ArcTanh[y,x] apparently is not, although ArcTanh[-y,-x] is a different angle. Your veto can stand, though Wiki is poorer for it. 195.92.168.168 09:50, 12 October 2005 (UTC)

Roger, I have no veto, only my judgement based on the arguments above. ArcTanh2 simply doesn't seem widely enough known or used to merit a mention in this article. --Macrakis 11:37, 12 October 2005 (UTC)

[edit] Unaccesable?

I thought wikipedia was supposed to be an easy to use encyclopedia, these won't be easy for anyone not studying maths to understand

I have added some additional explanatory text to the introduction of the article. I hope this helps, though there is no doubt room for more. Beyond that, it is true that the content gets moderately technical, but then this is a technical subject. --Macrakis 20:49, 19 October 2005 (UTC)

Thanks that has helped somewhat --Albert Einsteins pipe

[edit] Why is it defined so?

For

Could anyone tell me why? --HydrogenSu 07:48, 21 December 2005 (UTC)

Hyperbolic functions that are defined in terms of

e x

and

e - x

that bear similarities to the trigonometric (circular) functions. When plotted parametrically, trigonometric functions can be used to create circles. When plotted parametrically, hyperbolic functions can be used to create hyperbolas. That's the best explanation I can offer, as I've only recently been introduced to them. Deskana (talk) 19:25, 8 February 2006 (UTC)

well,

$\sin(x) := \frac{e^{ix} - e^{-ix}}{2i}$

sanity check:

e i π / 2 = i = > sin(π / 2) = 1

okay :) Now the hyperbolic variants are the same except without i. --MarSch 12:16, 3 May 2006 (UTC)

[edit] Names of inverses

It appears (from Google, etc.) that asinh etc. are the most common form of the inverse functions, not arsinh or arcsinh. WP doesn't try to prescribe best usage, but record actual usage. Thanks to SKvalen for pointing out that arcsinh is not the most common form. --Macrakis 02:54, 22 December 2005 (UTC)

If you take Google as a reference, please note that the reason for having the most hits for asinh etc. is that this is the way these functions are called in computer libraries. I've never seen a mathematician use asinh etc. --Tob 14:02, 4 January 2006 (UTC)

Tob is right. I was taught it was "arsinh". Deskana (talk) 19:26, 8 February 2006 (UTC)

who cares? 128.197.127.74

I've never seen the variants with only ar instead of arc before. Do we have a reference for this usage? Do we have any reference as to what usage should be preferred/is more prevalent? --MarSch 12:09, 3 May 2006 (UTC)

Scanning back up through talk, I see that or the hyperbolic variants ar shoud be preferred over arc. It would be good to have a source for this. --MarSch 12:21, 3 May 2006 (UTC)

Arc prefix is definitely wrong! It applies to trigonometric functions only.

Trigonometric functions are (or: can be) defined in terms of the unit circle's arc length as a parameter, so inverse trigonometric functions give the arc length as their value (output); that's why they are arc–functions, and their names have the arc prefix.

On the other hand, hyperbolic functions are (or: can be) defined in terms of some hyperbolic figure area as a parameter (see Image:Hyperbolic functions.svg), so inverse hyperbolic functions give an area as their value (output); that's why they are area–functions, and their names have ar prefix, distinct from trigonometric arc-functions. ---CiaPan 12:36, 22 October 2007 (UTC)

[edit] Plot Colors

The red and green in the plots are really bad for people who are color blind. Any chance somebody could redo them with more accessible colors?

Sure. What colors are better? I'm not colorblind, so I can't tell. --M1ss1ontom a rs2k4 ^{(T | C | @)} 01:11, 1 December 2006 (UTC)

As a rule of thumb, dark and deeply-saturated pure greens are a problem for most red-green people. Moving the hue more towards blue-green and/or desaturating the green are usually pretty effective. That might not cut it for blue-yellow people though. Generally, if your colors all have different brightness and saturation levels, you're probably OK. (Wikipedia should really have a set of recommended colors for diagrams and such.) Shaunm 20:37, 20 February 2007 (UTC)

[edit] calculus

I use maple and am not sure how to use latex. The article should give the differentials of sinh and cosh, writen in maple as: diff(sinh(x),x)=cosh(x); diff(cosh(x),x)=sinh(x); Sorry I cant edit it myself

<math> d \cosh(x) = \sinh(x), \; \; d \sinh(x) = \cosh(x) </math> as per Latex. Maple will convert output into latex code for you; see the help pages.---CH 16:14, 10 June 2006 (UTC)

You possibly meant LaTeX, CH? ;) --CiaPan 09:37, 11 November 2007 (UTC)

[edit] log on inverse functions.

log implies that this is to the base 10, when it is actually to the base e so i suggest that this is changed to ln.

In pure mathematics, log implies base e. But since this topic is relevant for non-mathematicians as well, you have a point. Fredrik Johansson 15:21, 21 August 2006 (UTC)

[edit] The Imaginary Unit

The article states that i is defined as the square root of -1, and that's incorrect. It's defined by i^2 = -1.

A fine case of tetrapilotomy. Yes, I guess we should distinguish between the positive and negative square roots of -1 (i.e. ±i). Urhixidur 03:15, 25 September 2006 (UTC)

[edit] Error in plot

Mmm, I think that there is an error in the image of the iperbola: sinh(a) should refer to the ordinate of the intercepta!
In fact $cosh 2 (a) - sinh 2 (a) = 1$ , and $\cosh(a) \ne 0$ always. I'm not changing it because I'm new at editing wikipedia, but if this message will not be answered in one week, I'll be back and mod it.

--Astabada 22:15, 28 October 2007 (UTC)

.......and that is exactly what the image shows. Hyp.sine is the length of the vertical red line, that is the ordinate. Hyp.cosine is the length of the horizontal red line, and it is always different from zero — hyperbola does not touch OY axis in any point. In fact it does not approach closer than to x=1, so cosh(a)≥1 always. --CiaPan 07:34, 29 October 2007 (UTC)
BTW I slightly corrected your LaTeX notation. CiaPan

.......yes, I'm sorry, it can be viewed in both ways... I would have written

sinh(a)

as near as possible to the Y axis, but I recognize it may depend on habits or conventions used in countries different from mine...

--Astabada 11:41, 29 October 2007 (UTC)

Right, that's a matter of habits. You can write the symbol at the axis if you want to emphasize the co-ordinate, or at the construction line if you want to emphasize the specific length. Tha latter is useful if some lengths are not perpendicular to any axis or the line does not start from an axis (see Image:Circle-trig6.svg for example).

In the case we discuss here both methods would be equivalent. --CiaPan 10:41, 30 October 2007 (UTC)