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FFTW: Difference between revisions

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This example shows the basic steps when using fftw.  
This example shows the basic steps when using fftw.  


Load the necessary module.  
Load the necessary module. For example, in case of gnu double precision version:
 
Example in case of the gnu double precision version:
{{Command| command =<nowiki>
{{Command| command =<nowiki>
module load numlib/fftw/3.3.2_double-openmpi-1.6-gnu-4.6.3
module load numlib/fftw/3.3.2_double-openmpi-1.6-gnu-4.6.3

Revision as of 09:58, 9 October 2012

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.
Fftw-logo.gif
Developer:
Platforms: NEC Nehalem Cluster
Category: Numerical Library
License: Open Source / GNU GPL
Website: FFTW Home Page


Using FFTW on Nehalem cluster:

There are four versions of FFTW instaled on Nehalem cluster:

  • intel single and double precision
  • gnu single and double precision

Example

This example shows the basic steps when using fftw.

Load the necessary module. For example, in case of gnu double precision version:

module load numlib/fftw/3.3.2_double-openmpi-1.6-gnu-4.6.3


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:

gcc 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_.

See also

External links