Hi!
I am using the fft() function the base package to transform some 1d signal. If I use this standar fucntion I get a very huge first fourier coeficient.
I think this dues to the handling of the borders of the signal.
Usually in fft especially in image processing the signal is simulated to be continuous by adding the signal several times periodically. My question is, is there some function implemented in R handling this or do I have to combine my data manually ?
Thanks,
The fft function computes the discrete transform
d(lambda) = SUM x(t) exp(-i * lambda * t)
(for a discrete set of lambda values).
The first coefficient is just SUM x(t). This means that the problem is not end-point discontinuity, but the fact that the average level of the signal is non-zero.
Replicating the series k times won't help, you'll just make the first coefficent k times bigger.
-- Ross Ihaka Email: [EMAIL PROTECTED] Department of Statistics Phone: (64-9) 373-7599 x 85054 University of Auckland Fax: (64-9) 373-7018 Private Bag 92019, Auckland New Zealand
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