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MathGroup Archive 2005

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Re: Extract Coefficients of Fourier Series

  • To: mathgroup at smc.vnet.net
  • Subject: [mg58823] Re: Extract Coefficients of Fourier Series
  • From: mike_in_england2000 at yahoo.co.uk
  • Date: Wed, 20 Jul 2005 00:29:21 -0400 (EDT)
  • References: <dbie2e$brj$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi

In order to illustrate how I went about this I created some random data
and TrigFit returned something like this.

0.576739 + 0.128598 Cos[x] + 0.0328485
  Cos[2 x] - 0.018517 Cos[3 x] + 0.0484222 Cos[4 x]

So I call this functiuon fit[x] -

fit[x_]:=0.576739 + 0.128598 Cos[x] + 0.0328485
  Cos[2 x] - 0.018517 Cos[3 x] + 0.0484222 Cos[4 x]

The constant term I get by doing
const = fit[x][[1]];

the rest of the terms I get using a loop:

Do[
  coeff = fit[x][[n]][[1]];
  Print[coeff];
  , {n, 2, Length[fit[x]]}
  ]

which should print out the coefficients.  I'll leave it to you to
modify the loop so instead of printing them you square and add them up.

hope this helps

Mike


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