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MathGroup Archive 1999

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Problem with the zero-term of Fourier[]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19606] Problem with the zero-term of Fourier[]
  • From: hans.steffani at e-technik.tu-chemnitz.de (Hans Steffani)
  • Date: Sat, 4 Sep 1999 21:09:14 -0400
  • Organization: Chemnitz University of Technology, GER
  • Sender: owner-wri-mathgroup at wolfram.com

If have a long list of measured values in ixr.
(Plus@@ixr)/Sqrt[Length[ixr]]
gives
-146.263

but
Fourier[ixr][[1]]
gives
-56.1317-3.03437 I

which is complex although it should be real (ixr is a list of 
real numbers) and it is different from the first term althugh
it should be the same. 

I also tried
1/Sqrt[Length[ixr]] *
  Sum[ixr[[tau]] Exp[2 Pi I(tau-1)(1-1)/Length[ixr]],{tau,Length[ixr]}]
which also gives -146.263

What is the problem?

Hans Friedrich Steffani

--
Hans Friedrich Steffani
Institut fuer Elektrische Maschinen und Antriebe, TU Chemnitz
mailto:hans.steffani at e-technik.tu-chemnitz.de
http://www.tu-chemnitz.de/~hfst/


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