Cross-Correlation with FFT

Hello,

how can i implement the fft in delphi 7?
i have two arrays with lot of numbers -> data.
i would realize this functions:

http://www.informatik.fh-wiesbaden.de/~linn/vpdv9900/ortgKorr/kk_theorem.gif

please help.

Thanks
Scorpie

Comments

  • : Hello,
    :
    : how can i implement the fft in delphi 7?
    : i have two arrays with lot of numbers -> data.
    : i would realize this functions:
    :
    : http://www.informatik.fh-wiesbaden.de/~linn/vpdv9900/ortgKorr/kk_theorem.gif
    :
    : please help.
    :
    : Thanks
    : Scorpie
    :
    Here is the code for the A() function, but I won't write all four. You need to figure out the other three.
    [code]
    function LargeA(n: integer; a: array of double; j: double): double;
    var
    t: integer;
    begin
    Result := 0;
    for i := 0 to High(a) do
    Result := Result + a[t]*exp(-2*j*pi*n*t/Length(a));
    end;
    [/code]
    I've used the same symbols as in the formula, so that shouldn't be a problem.
  • thanks for the fast answer,

    how can i define the "j", with wich value? it is the complex kostant. j=-1.
    how can i write the Z(n)=A(n)B*(n)? I know that B*(n)is the "konjugiert komplexe" from B(n), but how can i programming this?

    thanks a lot

    Scorpie
  • : thanks for the fast answer,
    :
    : how can i define the "j", with wich value? it is the complex kostant. j=-1.
    : how can i write the Z(n)=A(n)B*(n)? I know that B*(n)is the "konjugiert komplexe" from B(n), but how can i programming this?
    :
    : thanks a lot
    :
    : Scorpie
    :
    Delphi doesn't know how to handle complex numbers, but if memory serves me well I think you can write the exponent (exp(j)) into a sum of sin and cos with non-complex numbers. Just check with you math books on that. The "konjugiert komplexe" is can be calculated using a formula, but I don't know which (currently no math-books with me). Again this should be in a good math-book. I think it's something with the gaussian elimination method.
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