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fft_bench.cpp
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fft_bench.cpp
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//#include <stdio.h>
//#include <iostream>
#include <mpi.h>
#include <fftw3.h>
#include <cstdlib>
#include <limits>
#include <cmath>
using namespace std;
int main(int argc, char *argv[])
{
MPI_Init(&argc, &argv);
long N = atol(argv[1]);
long n = N * N;
fftw_complex *data;
fftw_plan p, q;
data = (fftw_complex*) fftw_malloc(sizeof(fftw_complex) * n);
int length[] = {N};
p = fftw_plan_many_dft(1, length, N, data, length, 1, N,
data, length, 1, N, FFTW_FORWARD, FFTW_ESTIMATE);
q = fftw_plan_many_dft(1, length, N, data, length, 1, N,
data, length, 1, N, FFTW_BACKWARD, FFTW_ESTIMATE);
srand48(0);
for(int i = 0; i<n; i++) {
data[i][0] = drand48();
data[i][1] = drand48();
}
double t1, t2;
t1 = MPI_Wtime();
fftw_execute(p);
t2 = MPI_Wtime() - t1;
printf( "On %ld elements, Elapsed time is %f with %f Gflop/s\n", n, t2, 5*(double)n*log2((double)n)/(t2*1000000000));
fftw_execute(q);
double infNorm = 0.0;
srand48(0);
for(int i=0; i<n; i++) {
data[i][0] = data[i][0]/N - drand48();
data[i][1] = data[i][1]/N - drand48();
double mag = sqrt(pow(data[i][0],2) + pow(data[i][1], 2));
if(mag > infNorm) infNorm = mag;
}
double r = infNorm / (std::numeric_limits<double>::epsilon() * log((double)n));
printf("residual = %f\n", r);
fftw_destroy_plan(p);
fftw_destroy_plan(q);
fftw_free(data);
MPI_Finalize();
return 0;
}