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FFTW
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| FFTW (Fastest Fourier Transform in the West) is a free collection of fast C routines for computing the Discrete Fourier Transform in one or more dimensions. It includes complex, real, symmetric and parallel transforms and can handle arbitrary array sizes efficiently. FFTW is typically faster than other publically-available FFT implementations and is even competitive with vendor-tuned libraries. |
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Using FFTW on Nehalem cluster
The library has been compiled with type-prefix for both single and double precision.
There are two versions of FFTW instaled on Nehalem cluster:
- intel
- gnu
Example
This example shows the basic steps when using fftw.
Load the necessary module. For example:
module load numlib/fftw/3.3.2-typeprefix-openmpi-1.6-intel-12.1.5
Simple example
File: ex1_fftw.c
/*
* fft.c: compute FFT and IFFT from an array
*/
#include <stdio.h>
#include <fftw3.h>
#define SIZE 4
int main( int argc, char** argv )
{
double input[SIZE] = { 1.0, 1.0, 1.0, 1.0 };
fftw_complex *data, *fft_result, *ifft_result;
fftw_plan plan_forward, plan_backward;
int i;
data = ( fftw_complex* ) fftw_malloc( sizeof( fftw_complex ) * SIZE );
fft_result = ( fftw_complex* ) fftw_malloc( sizeof( fftw_complex ) * SIZE );
ifft_result = ( fftw_complex* ) fftw_malloc( sizeof( fftw_complex ) * SIZE );
plan_forward = fftw_plan_dft_1d( SIZE, data, fft_result, FFTW_FORWARD, FFTW_ESTIMATE );
plan_backward = fftw_plan_dft_1d( SIZE, fft_result, ifft_result, FFTW_BACKWARD,
FFTW_ESTIMATE );
/* populate input data */
for( i = 0 ; i < SIZE ; i++ ) {
data[i][0] = input[i];
data[i][1] = 0.0;
}
/* print initial data */
for( i = 0 ; i < SIZE ; i++ ) {
fprintf( stdout, "data[%d] = { %2.2f, %2.2f }\n",
i, data[i][0], data[i][1] );
}
fftw_execute( plan_forward );
/* print fft result */
for( i = 0 ; i < SIZE ; i++ ) {
fprintf( stdout, "fft_result[%d] = { %2.2f, %2.2f }\n",
i, fft_result[i][0], fft_result[i][1] );
}
fftw_execute( plan_backward );
/* print ifft result */
for( i = 0 ; i < SIZE ; i++ ) {
fprintf( stdout, "ifft_result[%d] = { %2.2f, %2.2f }\n",
i, ifft_result[i][0] / SIZE, ifft_result[i][1] / SIZE );
}
/* free memory */
fftw_destroy_plan( plan_forward );
fftw_destroy_plan( plan_backward );
fftw_free( data );
fftw_free( fft_result );
fftw_free( ifft_result );
return 0;
}
Compile with
icc ex1_fftw.c -o ex1 -I/$FFTW_HOME/include -L/$FFTW_HOME/lib -lfftw3
(lfftw3f for single version)
The shell variable $FFTW_HOME is available after loading the required modules.
For the single precision version all FFTW identifiers will begin with fftwf_ instead of fftw_.