FFTW

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.

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 (example in case of the intel double precision version):

module load compiler/gnu/4.4.3 module load compiler/intel/11.1 module load mpi/openmpi/1.4.1-intel-11.1 (only if mpi programs are compiled) module load numlib/fftw/3.2.2_double-openmpi-1.4.1-intel-11.1

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 gnu fftw version you need the gnu version of the mpi module if mpi programs are compiled.

For the single precision version all FFTW identifiers will begin with fftwf_ instead of fftw_.

See also

• Software Development Tools, Compilers & Libraries

External links

• FFTW Home Page