Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2007

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

Search the Archive

Frequency response function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg82755] Frequency response function
  • From: Will Robertson <wspr81 at gmail.com>
  • Date: Tue, 30 Oct 2007 03:36:29 -0500 (EST)

Hello,

People have asked in the past for how to plot a power spectral density
plot, or a frequency response plot, or whatever you like to call it.
Since there isn't an archive of a good solution on this newgroup,
here's a quick and basic solution that I just put together:

FRF[signal_, tt : {t_, tmin_, tmax_, tstep_}] :=
 Module[{s, list, fft, N, L, freq},
  (* Generate the signal and its DFT: *)
  list = Table[signal, tt];
  fft = Abs[Chop@Fourier@list]^2;
  (* Get the number of samples and throw away the wraparound: *)
  N = Length[list];
  L = If[OddQ[N], (N - 1)/2, N/2];
  fft = Take[fft, L];
  (* Scale the frequencies and plot the FRF: *)
  freq = Range[L]/(N tstep);
  ListLogPlot[Transpose@{freq, fft}, PlotRange -> All,
   Joined -> True]
  ]
With[{\[Omega] = 2},
 FRF[Sin[2 \[Pi] \[Omega] t] + Sin[2 \[Pi] 10 \[Omega] t], {t, 0, 10,
   1/50}]]

(Modifiable & distributable under the Apache License v2.)
Obviously this is just a "first pass" at the many many features that
should be added to such a function (such as padding, windowing,
support for complex data even!). I don't even know if it works
correctly for tmin != 0.

I'd be great for people to post their own improvements in this thread.
Eventually I might make a package out of the whole thing. (A port of
the spectral density routines here would be ideally the best: <http://
www.mecheng.adelaide.edu.au/~pvl/octave/>)

Cheers,
Will



  • Prev by Date: Re: Use of FrameLabel for GraphicsGrid
  • Next by Date: Re: Bug of Integrate
  • Previous by thread: Re: FindRoot and Bose-Einstein distribution
  • Next by thread: Re: Creating and installing one's own packages?