fftw

Arguments

y,x

matrix/vector of real/complex data. Input/output data to be transformed.

sign

Integer. 1 or -1. Set direct or inverse transform.

dim

integer. Set the dimension (the length) of the transform.

incr

integer. Set the stride (the span) of the transform.

Description

This function realizes direct/inverse Discrete Fourier Transform (DFT) with the help of the FFTW library.

One can compute vector, 2D, M-D transform with this function.

For more details of fftw syntax see fft scilab function.

For more details about FFTW library see FFTW Web site : http://www.fftw.org

Remark: fftw function automatically stores his last parameters in memory to re-use it in a second time.

This improves greatly the time computation when consecutives calls (with same parameters) are performed.

Examples

//simple vector direct transform
a = rand(50,1)+%i*rand(50,1);
y = fftw(a);
y = fftw(a,-1);
//inverse transform
b = fftw(y,1);

//2D transform
a = rand(512,512)+%i*rand(512,512);
y = fftw(a);

//M-D transform -old calling sequence-
a = rand(120,1);
y = a;
dim=[5 6 4];incr=[1 5 30];
for i=1:3
  y = fftw(y,-1,dim(i),incr(i));
end

//M-D transform -new calling sequence-
//More efficient than old
y = fftw(a,-1,[5 6 4],[1 5 30]);
b = fftw(y,1,[5 6 4],[1 5 30]);

See Also

• fftw_flags — set computation method of fast fourier transform of the fftw function
• get_fftw_wisdom — return fftw wisdom
• set_fftw_wisdom — set fftw wisdom
• fftw_forget_wisdom — Reset fftw wisdom

Bibliography

Matteo Frigo and Steven G. Johnson, "FFTW Manual fo version 3.1.2" June 2006. Available : http://www.fftw.org