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FFTW: Difference between revisions

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| logo = [[Image:fftw-logo.gif]]
| logo = [[Image:fftw-logo.gif]]
| developer              =  
| developer              =  
| available on      = [[NEC Nehalem Cluster]]
| available on      = [[Vulcan (NEC Cluster)]]
| category          = [[:Category:Numerical Library | Numerical Library]]
| category          = [[:Category:Numerical Library | Numerical Library]]
| license            = Open Source / GNU GPL
| license            = Open Source / GNU GPL
Line 9: Line 9:
}}
}}


== Using FFTW on Nehalem cluster: ==
=== Using FFTW on Vulcan (NEC cluster) ===
There are four versions of FFTW instaled on Nehalem cluster:
The library has been compiled with type-prefix for both single and double precision.
* intel single and double precision
 
* gnu single and double precision
There are two versions of FFTW instaled on Vulcan:
* intel  
* gnu  


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


Load the necessary module (example in case of the intel double precision version):
Load the necessary module. For example:
{{Command| command =<nowiki>
{{Command| command =<nowiki>
module load compiler/gnu/4.4.3
module load numlib/fftw/3.3.2-typeprefix-openmpi-1.6-intel-12.1.5
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
</nowiki>
</nowiki>
}}
}}


=== Simple example ===


{{File|filename = ex1_fftw.c
{{File|filename = ex1_fftw.c
Line 49: Line 49:


           plan_forward  = fftw_plan_dft_1d( SIZE, data, fft_result, FFTW_FORWARD, FFTW_ESTIMATE );
           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 );
           plan_backward = fftw_plan_dft_1d( SIZE, fft_result, ifft_result, FFTW_BACKWARD,  
                                            FFTW_ESTIMATE );


           /* populate input data */
           /* populate input data */
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</pre>}}
</pre>}}


Compile with:
=== Compile with ===
{{Command| command = gcc ex1_fftw.c -o ex1 -I/$FFTW_HOME/include -L/$FFTW_HOME/lib -lfftw3
 
{{Command| command = icc ex1_fftw.c -o ex1 -I/$FFTW_HOME/include -L/$FFTW_HOME/lib -lfftw3


(lfftw3f for single version)
(lfftw3f for single version)
}}
}}
The shell variable $FFTW_HOME is available after loading the required modules.
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_.
For the single precision version all FFTW identifiers will begin with fftwf_ instead of fftw_.

Latest revision as of 11:36, 18 August 2021

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: Vulcan (NEC Cluster)
Category: Numerical Library
License: Open Source / GNU GPL
Website: FFTW Home Page


Using FFTW on Vulcan (NEC cluster)

The library has been compiled with type-prefix for both single and double precision.

There are two versions of FFTW instaled on Vulcan:

  • 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_.

See also

External links