Element wise multiplication of two arrays in C/C++
I would like to perform Element wise multiplication of two arrays, both are of type complex but I am getting the following error message:
serge@ubuntu:~/Downloads/OpenCV/opencv-2.4.9/build$ g++ -o myfft myfft.cpp -std=c++14
In file included from myfft.cpp:14:0:
cs_delay.cpp: In function ‘void cs_delay(CArray&, int, int, int)’:
cs_delay.cpp:35:28: error: no match for ‘operator*’ (operand types are ‘void’ and ‘Complex {aka std::complex}’)
x[j] = ifft(fft(x) * rot[j]);
^
cs_delay.cpp:35:28: note: candidates are:
In file included from myfft.cpp:1:0:
/usr/include/c++/4.9/complex:381:5: note: template std::complex std::operator*(const std::complex&, const std::complex&)
operator*(const complex& __x, const complex& __y)
^
/usr/include/c++/4.9/complex:381:5: note: template argument deduction/substitution failed:
In file included from myfft.cpp:14:0:
cs_delay.cpp:35:35: note: mismatched types ‘const std::complex’ and ‘void’
x[j] = ifft(fft(x) * rot[j]);
^
In file included from myfft.cpp:1:0:
/usr/include/c++/4.9/complex:390:5: note: template std::complex std::operator*(const std::complex&, const _Tp&)
operator*(const complex& __x, const _Tp& __y)
^
/usr/include/c++/4.9/complex:390:5: note: template argument deduction/substitution failed:
In file included from myfft.cpp:14:0:
cs_delay.cpp:35:35: note: mismatched types ‘const std::complex’ and ‘void’
x[j] = ifft(fft(x) * rot[j]);
^
In file included from myfft.cpp:1:0:
/usr/include/c++/4.9/complex:399:5: note: template std::complex std::operator*(const _Tp&, const std::complex&)
operator*(const _Tp& __x, const complex& __y)
^
/usr/include/c++/4.9/complex:399:5: note: template argument deduction/substitution failed:
In file included from myfft.cpp:14:0:
cs_delay.cpp:35:35: note: deduced conflicting types for parameter ‘_Tp’ (‘void’ and ‘double’)
x[j] = ifft(fft(x) * rot[j]);
^
In file included from /usr/include/c++/4.9/valarray:587:0,
from myfft.cpp:3:
/usr/include/c++/4.9/bits/valarray_after.h:404:5: note: template std::_Expr, typename std::__fun::result_type> std::operator*(const std::_Expr&, const std::_Expr&)
_DEFINE_EXPR_BINARY_OPERATOR(*, __multiplies)
^
/usr/include/c++/4.9/bits/valarray_after.h:404:5: note: template argument deduction/substitution failed:
In file included from myfft.cpp:14:0:
cs_delay.cpp:35:35: note: mismatched types ‘const std::_Expr’ and ‘void’
x[j] = ifft(fft(x) * rot[j]);
^
In file included from /usr/include/c++/4.9/valarray:587:0,
from myfft.cpp:3:
/usr/include/c++/4.9/bits/valarray_after.h:404:5: note: template std::_Expr, typename std::__fun::result_type> std:Function which returns error :
//cs_delay.cpp
using namespace std;
typedef std::complex<double> Complex;
typedef std::valarray<Complex> CArray;
void cs_delay(CArray& x, int rate_hz, int delay_s, int n)
{
const size_t N = x.size();
if (N <= 1) return;
int j;
double cycLen_s;
double nCyc;
double* f = new double[n];
double* phase = new double[n];
Complex* rot = new Complex[n];
cycLen_s = n/rate_hz;
nCyc = delay_s / cycLen_s;
/*************************************************************/
for ( j = 0 ; j < n ; j++ ){
f[j] =j+floor(n/2);
f[j] =fmod(f[j], n);
f[j] =f[j]-floor(n/2);
phase[j] = -2 * PI * f[j] * nCyc;
rot[j] = exp(1i*phase[j]);
std::cout << "rot["<<j<<"] ="<<rot[j] <<std::endl;
fft(x);
x *= rot[j];
ifft(x);
}
/*************************************************************/
delete [] f;
delete [] phase;
delete [] rot;
}
fft and ifft are here:
//fft.cpp
using namespace std;
const double PI = 3.141592653589793238460;
//functions declarations
typedef std::complex<double> Complex;
typedef std::valarray<Complex> CArray;
// Cooley–Tukey FFT (in-place, divide-and-conquer)
// Higher memory requirements and redundancy although more intuitive
void fft(CArray& x)
{
const size_t N = x.size();
if (N <= 1) return;
// divide
CArray even = x[std::slice(0, N/2, 2)];
CArray odd = x[std::slice(1, N/2, 2)];
// conquer
fft(even);
fft(odd);
// combine
for (size_t k = 0; k < N/2; ++k)
{
Complex t = std::polar(1.0, -2 * PI * k / N) * odd[k];
x[k ] = even[k] + t;
x[k+N/2] = even[k] - t;
}
}
// inverse fft (in-place)
void ifft(CArray& x)
{
// conjugate the complex numbers
x = x.apply(std::conj);
// forward fft
fft( x );
// conjugate the complex numbers again
x = x.apply(std::conj);
// scale the numbers
x /= x.size();
}
here is my main function:
#include <complex>
#include <iostream>
#include <valarray>
#include <malloc.h>
#include <string>
#include <stdlib.h>
#include <fstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <iomanip>
#include <cmath>
#include "fft.cpp"
#include "cs_delay.cpp"
using namespace std;
//const double PI = 3.141592653589793238460;
char filename[] = "vidres6.txt";
char filename2[] = "vidres7.txt";
//typedef std::complex<double> Complex;
//typedef std::valarray <Complex> CArray;
/***********************************************************************************************
* function declarations
************************** ******************************************************** ***********/
void fft(CArray& x);
void ifft(CArray& x);
void binFreq(int n);
void cs_delay(CArray& x, int rate_hz, int delay_s, int n);
int main()
{
int dTest_samples;
int cTest;
//cTest = -cTest;
int n=299;
int i;
int j;
double x [n];
/*****************************getting x*******************************/
string line;
double Result;
ifstream myfile (filename);
if (myfile.is_open())
{
for ( i = 0 ; (i < n) && (myfile >> x[i]) ; ++i)
cout << line << 'n';
stringstream convert(line);
if ( !(convert >> Result) )
Result = 0;
x[i]=Result;
}
else cout << "Unable to open file";
/***********************************************************************/
Complex test[n];
for ( i = 0 ; i < n ; ++i )
test[i] = x[i];
CArray data(test,n);
// forward fft
fft(data);
std::cout << "fft" << std::endl;
for (int i = 0; i <n; ++i)
{
cout << data[i] << endl;
}
// inverse fft
ifft(data);
std::cout << std::endl << "ifft" << std::endl;
for (int i = 0; i <n; ++i)
{
std::cout << data[i] << std::endl;
}
return 0;
}
fft does not return anything (it returns void ) but you are trying to multiply the result by something (" fft(x) * rot[j] "). This is not going to work.
On the same line, you assign the result of ifft to x[j] , but ifft also does not return anything.
Assuming that fft and ifft are modifying their arguments in-place correctly, try replacing the line
x[j] = ifft(fft(x) * rot[j]);
by
fft(x);
x *= rot[j];
ifft(x);
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