z <- rnorm(5000) f <- fft(z) d <- fft(f, inverse=T) plot(z, d) z <- rnorm(5000) z.ts <- ts(z) f <- fft(z.ts) d <- fft(f, inverse=T) plot(z.ts, d)
temp <- matrix(c(1,4,2, 20), nrow=2) d <- fft(temp) f <- fft(d, inverse=T) plot(temp, f) this, looks to me, to be the same. you have to take the inverse of the fft to get the original series. I don't know anything about matlab but it looks like the imaginary part is hidden. On Thu, Jul 31, 2008 at 5:12 PM, Li Li <[EMAIL PROTECTED]> wrote: > 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 < [EMAIL PROTECTED]> 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 >> > > [[alternative HTML version deleted]] > > ______________________________________________ > [EMAIL PROTECTED] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- Let's not spend our time and resources thinking about things that are so little or so large that all they really do for us is puff us up and make us feel like gods. We are mammals, and have not exhausted the annoying little problems of being mammals. -K. Mullis ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
