Talk:Heaviside step function

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  • What is the Fourier transform of the Heaviside function?

The definition is self-contradictory: Who can correct it?
S.

Dirac delta function also defines it, with the ≥ switched for a ≤ - but this still doesn't match the written definition, unless I was lied to by years of math teachers and zero is negative. --Brion 08:55 Oct 26, 2002 (UTC)


Looked it up, it's =1 at zero (your teachers were right, Brion, zero, is neither neg nor pos). Funnily enough, the book I have here, they give the positive part first, then the negative, which seems the wrong way round. If I remember correctly, the value at zero isn't crucial, and different definitions exist: can be H(0)=0, H(0)=1, and H(0)=0.5 and of course, H(0)=cream cheese. needs checking though. -- Tarquin 10:16 Oct 26, 2002 (UTC)


In Japan, it is thought that

\int^{0}_{-\epsilon} \delta(x) dx = \int^{+\epsilon}_{0} \delta(x) dx = 1/2 for all ε > 0

and every image H(x) of Heaviside step function H : \mathbb{R} \ni x \longrightarrow H(x) \in H(\mathbb{R}) \subset \mathbb{R} is

H(x) = \int^{x}_{-\infin} \delta(\xi) d\xi = \left\{\begin{matrix} 0 & \left( x < 0 \right) \\ 1/2 & \left( x = 0 \right) \\ 1 & \left( x > 0 \right) \end{matrix}\right. .

Koiki Sumi 00:00 15 Sep 2003 (UTC)

I kind of doubt there's any agreement at all, even in Japan...

Contents

[edit] fourier transform?

i can't find the fourier transform of the heaviside function anywhere...anyone willing to share their expertise :)

Comment at support.

Charles Matthews 13:59, 31 Jan 2004 (UTC)

Reminds me: I once won five pints of beer on a bet that it was in the textbooks (and drank three of them). As for the comment below, what is in 'the books' is typically wrong or misleading. I suppose the article can try to explain why. Charles Matthews 14:55, 11 Dec 2004 (UTC)

[edit] "integral representation of the step function"

I was prettying up that "integral representation of the step function" at the end, and upon looking at it, i don't think it's correct. maybe it is for the Signum function , but i don't think it is for the step function. BTW, if we define the step function strictly in terms of the sgn(), i think the Fourier Transform of it comes out nicely. also, the step function should either be undefined for x=0 or be defined to be 1/2 at x=0, but not either 1 or 0. r b-j 03:30, 11 Dec 2004 (UTC)

[edit] Fourier transform of the Heaviside Step Function

At the following address you will find the Fourier transform of the Heaviside Step Function http://mathworld.wolfram.com/HeavisideStepFunction.html

Hmmm - I'm not saying that's wrong. I would say that 1/x is not a locally integrable function. Therefore using it to represent a Schwartz distribution is not in itself a naive kind of definition. The formula therefore needs some commentary: the difference of the delta function and the reciprocal function is a combination that seems to require some discussion. Charles Matthews 12:48, 19 Apr 2005 (UTC)

[edit] The function letter?

Why is the function letter in this article a "u"? Everywhere else i've seen an H instead.Boothinator 23:11, 26 Apr 2005 (UTC)

I was taught with a u. Probably another one of those engineer/mathematcian differences. - Omegatron 23:51, Apr 26, 2005 (UTC)
Of all the pages linking here, Dirac delta function, Distribution, Continuous Fourier transform, Sufficiency (statistics), Negative and non-negative numbers, Green's function, Sign_function (actually uses h()), Rectangular function and Uniform distribution (continuous) use the H() notation while Z-transform, Two-sided Laplace transform, User:Jacobolus/coordinates and Coordinates (elementary mathematics) use the u() notation. Recurrence plot uses a Θ(). To me, it looks like the H() notation should be used to be more consistant with the rest of Wikipedia.Boothinator 00:52, 27 Apr 2005 (UTC)
I've seen H and θ. The different notations should be mentioned and referenced. --MarSch 13:12, 30 April 2006 (UTC)
I think that H is the most commonly used notation in mathematics and θ in physics. Md2perpe 10:39, 3 August 2006 (UTC)
...and I think that u(t) is the most common definition is signal processing. I, too, would support a consistent definition throughout Wikipedia. I personally like H(t).--Rabbanis 20:46, 8 August 2006 (UTC)
u is more familiar to me, of course, but if a majority of articles use h I guess that's ok. I wonder if u is used to distinguish it from H(f) = Hilbert transform? — Omegatron 21:13, 8 August 2006 (UTC)

It started out as H and was changed here. I would prefer H unless you have any objections? Rex the first talk | contribs 17:14, 20 May 2006 (UTC)

I support that different notation should be mentioned. I noticed σ notation, also. --Čikić Dragan (talk) 16:04, 21 February 2008 (UTC)

[edit] Analytic Exact Form of Unit Step Function

I removed this:

There are some trials to put analytical functions to numerically calculate Unit Step Function. The study published on [1] has shown that it is possible to mimic the Unit Step Function. The results were verified using Mathematica software.

It's uninteresting, of restricted applicability, (strictly speaking) incorrect (the inverse trigonometric functions do not have unique definitions) and constitutes original research. EdC 15:14, 4 June 2006 (UTC)

[edit] H(0) in the intro paragraph

It feels wrong to define H(0) as 1/2 and then immediately say the H(0) seldom matters and can be defined in various ways. However, it would also feel wrong to show a definition by case analysis which considered only x<0 and x>0. Would it be a horrible idea simply to remove the first displayed formula and just rely on the prose in the first sentence, plus the graph? Henning Makholm 01:37, 26 November 2006 (UTC)