- frequency analysing with Xi -
Xi supports multi dimensional fast fourier transform. As a reminder: fast fourier transform is a multi grid algorithm to compute the fourier transform of a function. It performs like N*log(N) (compare with N*N for the brute forward algorithm). I.e. the fast fourier transform of a rect signal can be evalutated by
( 1)>x=dincarr(100); ( 2)>double y[100]; ( 3)>y[25..74]=1; ( 4)>f=fft(y); ( 5)>plot(x,real(f),\curve);The result will look something like this (depends on your Xi-version;-)
To compute the backward fourier transform use
( 6)>b=rev_fft(f);