Services & Resources / Wolfram Forums
MathGroup Archive
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 1998

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: FourierTransform on UnitStep

  • To: mathgroup at
  • Subject: [mg14473] Re: FourierTransform on UnitStep
  • From: John Doty <jpd at>
  • Date: Fri, 23 Oct 1998 20:58:51 -0400
  • Organization: Wampler-Doty Family
  • References: <70k58j$>
  • Sender: owner-wri-mathgroup at

Normand Leclerc wrote:

>   I am a new EE Student and I'm just begining with Fourier transforms. I
> was using Mathematica at school when I saw something I just couldn't
> figure out.
>   FourierTransform[UnitStep[t],t,w] gives me I/w + pi DiracDelta[w]
>   I learned that it should give me pi DiracDelta[w]-I/w or 1/Iw + pi
> DiracDelta[w].
> Am I missing something or is there a bug in the FourierTransform
> package?  They are using Mathematica 3.0

There are two conventions for the sign of I in Fourier analysis: the
"physics" convention, and the "EE" convention. Mathematica uses the
"physics" convention.

If you set:

$FourierFrequencyConstant = -1

you'll get the behavior you want.

This clash of conventions often causes serious headaches. I have heard
that a certain array processor manufacturer once, in response to a
customer complaint, changed their firmware to use the "correct"
convention (according to that customer), without changing the
documentation or otherwise disseminating news of this change. As a
result, geologists interpreting the first synthetic aperture radar maps
of Venus from the Magellan mission struggled to find a geological
explanation for unexpected small-scale smoothness of the planet (the
problem was eventually discovered).

Be careful!

John Doty		"You can't confuse me, that's my job." Home: jpd at
Work: jpd at

  • Prev by Date: Re: Too Tny Fonts! in fractions, summations, etc.
  • Next by Date: Re: Inserting/Removing Forced Page Breaks?
  • Previous by thread: Re: FourierTransform on UnitStep
  • Next by thread: Re: FourierTransform on UnitStep