Message-ID: <8A5A60F7-A308-48DE-BBE6-7E211D0FA83A@dcn.davis.ca.us>
Date: 2021-03-22T16:32:47Z
From: Jeff Newmiller
Subject: Weird (wrong?) result for fft
In-Reply-To: <CAG0gC1eU0R3Rz-q=T9riVZUrQ8h22HG9d20wtH99Z=r2SdAu2w@mail.gmail.com>
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 described in ?complex.
On March 22, 2021 9:17:11 AM PDT, Filippo Monari <ingfimo at gmail.com> wrote:
>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 -2-2i
>
>> ft(fft(x), inverse = TRUE)/length(x)
>[1] 1+0i 2+0i 3+0i 4+0i
>
>Am I doing something wrong or is there a bug somewhere?
>
>Regards,
>Filippo
>
> [[alternative HTML version deleted]]
>
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--
Sent from my phone. Please excuse my brevity.