fourier transforms
- To: mathgroup at smc.vnet.net
- Subject: [mg17427] fourier transforms
- From: lucas <lucas at rutchem.rutgers.edu>
- Date: Thu, 6 May 1999 02:44:30 -0400
- Organization: Rutgers University
- Sender: owner-wri-mathgroup at wolfram.com
hello,
i am trying to do some fourier transforms with mathematica 3.0. i does
not behave as i expect, but perhaps i expect too much or do not
understand enough of mathematica. anyway, check this out.
f[x] = Exp[-m x]
<<Calculus`FourierTransform`
FourierCosTransform[f[x],x,a]
is supposed to return
m/(m^2 + a^2) when m > 0
but instead it returns the original FourierCosTransform[E^(-m x),x,a],
which any dummy can figure out.
which mathematica will return the proper result when manually done via
Integrate[f[x] Cos[a x],{x,0,Infinity}]
so i do not understand why it does not work. the same f[x] will work
properly if put under the FourierSinTransform and the manual
Integrate[f[x] Sin[a x],{x,o,Infinity}] which yields the result a/(m^2 +
a^2).
so i do not understand, why the FourierCosTransform does not work.
also, could i not use FourierTransform to convert a fxn from the time
domain to the frequency domain, like sin[t]. i can not get
FourierTransform to work on such a simple fxn either.
thank you in advance and have a nice day.
lucas