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    FAST FOURIER TRANSFORM

    - 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);
    


    Rechts Index Index Index Linls © 1995 by Bodo Junglas, Klaus Spanderen and Fabian Weis
    - Last revised: April 23 1996