Hi Filippo,
Why do you expect these two expressions to produce the same output?
Especially the second expression contains the first expression. There is no
way to have the same result unless the function "fft( * , inverse = TRUE)"
does nothing but multiplies the input by the input's length. It
Neither. The discrete Fourier transform is a complex number operation. R-help
is per the Posting Guide not an appropriate place to discuss theory in depth,
and there is plenty of theory in this question and practically no R, but you
can examine your result more closely with the functions
Hi all,
I am plying around with fft function from the stats package.
Running the example that is listed in the documentation:
x <- 1:4
fft(x) #output 1
fft(fft(x), inverse = TRUE)/length(x) #output 2
I was expecting that output 1 and two were the same but I get:
> fft(x)
[1] 10+0i -2+2i -2+0i
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