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

[Li Li]

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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