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fftcheck.c
Go to the documentation of this file.00001
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00007 #include "mrilib.h"
00008
00009 int main( int argc , char * argv[] )
00010 {
00011 int N ;
00012 complex * cx , * cs ;
00013 int ii ;
00014 float f , sum , xx,yy ;
00015
00016 if( argc < 3 ){ printf("Usage: fftcheck N nfreq | more\n"); exit(1); }
00017
00018 N = strtod( argv[1] , NULL ) ;
00019
00020 if( N > 0 && N != csfft_nextup(N) ){
00021 fprintf(stderr,"Can't do FFT of length %d\n",N) ; exit(1) ;
00022 } else if ( N < 0 ){
00023 N = -N ;
00024 }
00025
00026 f = strtod( argv[2] , NULL ) / N ;
00027
00028 cs = (complex *) malloc(sizeof(complex)*N) ;
00029 cx = (complex *) malloc(sizeof(complex)*N) ;
00030
00031 for( ii=0 ; ii < N ; ii++ ){
00032 cx[ii].r = cos(2*PI*f*ii) ; cx[ii].i = sin(2*PI*f*ii) ;
00033 cs[ii] = cx[ii] ;
00034 }
00035
00036 csfft_scale_inverse(1) ;
00037
00038 csfft_cox( -1 , N , cx ) ;
00039
00040 for( ii=0 ; ii < N ; ii++ )
00041 printf("%2d: %12.5g %12.5g\n" , ii , cx[ii].r , cx[ii].i ) ;
00042
00043 csfft_cox( 1 , N , cx ) ;
00044 sum = 0.0 ;
00045 for( ii=0 ; ii < N ; ii++ ){
00046 xx = cx[ii].r - cs[ii].r ;
00047 yy = cx[ii].i - cs[ii].i ; sum += xx*xx + yy*yy ;
00048 }
00049 sum = sqrt( sum/N ) ;
00050 printf("RMS error = %g\n",sum) ;
00051 exit(0) ;
00052 }
