How to use FFTW

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How to compute FFT using FFTW in Qt

Getting Start

Note that I do this in Ubuntu operating system, in Windows some steps are different.

• Step1: Download FFTW ([[1]])

• Step2: Extract and Configure it (my path: /home/jafarabadi/Documents/fftw-3.3.4)

cd /home/jafarabadi/Documents/fftw-3.3.4
chmod +x configure
./configure
make
make install

• Step 3: Add library to project: first open [your_project_name].pro file in Qt Creator and add this line:

LIBS += -lfftw3

• Step 4: Example

#include <fftw3.h>
int N;

// Set N to the number of complex elements in the input array

fftw_complex *in, *out;
in = (fftw_complex *)fftw_malloc(sizeof(fftw_complex) * N);
out = (fftw_complex *)fftw_malloc(sizeof(fftw_complex) * N);

// Initialize 'in' with N complex entries

fftw_plan my_plan;
my_plan = fftw_plan_dft_1d(N, in, out, FFTW_FORWARD, FFTW_ESTIMATE);
fftw_execute(my_plan);

// Use 'out' for something

fftw_destroy_plan(my_plan);
fftw_free(in);
fftw_free(out);

// A short tutorial: http://www2.math.uu.se/~figueras/fftw_tutorial/text/fftw_tutorial.pdf