Re: [R] Is R's fast fourier transform function different from "fft2" in Matlab?

From: Li Li <lilycai2007_at_gmail.com>
Date: Wed, 02 May 2007 22:53:55 -0400

Thanks for both replies.
Then I found the "ifft2" from Matlab gives different result from "fft( , inverse=T)" from R.
An example:
in R:
> temp <- matrix(c(1,4,2, 20), nrow=2)
> fft(temp)

       [,1] [,2]
[1,] 27+0i -17+0i
[2,] -21+0i 15+0i
> fft(temp,inverse=T)

       [,1] [,2]
[1,] 27+0i -17+0i
[2,] -21+0i 15+0i

In Matlab:
> A = [1,2;4,20];
> fft2(A)
Ans =

   27 -17
  -21 15
>ifft2(A)

Ans=

   6.7500 -4.2500
  -5.2500 3.7500

I also tried mvfft with inverse but can't get same result with "ifft2". Does any function work?
Thanks,

Li

On 5/2/07, Sundar Dorai-Raj < sundar.dorai-raj_at_pdf.com> wrote:
>
>
> I don't know Matlab or any of its functions, but the following produces
> the same output.
>
> z <- matrix(c(1, 4, 2, 20), nrow = 2)
> Re(fft(z))
>
> And from ?fft:
>
> When 'z' contains an array, 'fft' computes and returns the multivariate
> (spatial) transform.
>
> HTH,
>
> --sundar
>

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