Eigen::FFT<float> fft;

std::vector<float> result;

std::vector<complex<float> > fv1;

std::vector<complex<float> > fv2;

std::vector<complex<float> > mulvec;

//computes cumulative length of r1 and r2;

size_t N = r1.size() + r2.size() - 1 ;

size_t M = fft_next_good_size(N);

//padds signals with zeros

while( r1.size() != M ) r1.emplace_back(0.0);

while( r2.size() != M ) r2.emplace_back(0.0);

//Performs FWD FFT1

fft.fwd(fv1, r1);

//Performs FWD FFT2

fft.fwd(fv2, r2);

//multiply FV1 * FV2, element-wise

std::transform( fv1.begin(), fv1.end(),

fv2.begin(), std::back_inserter(mulvec),

std::multiplies< complex<float> >() );

//FFT INVERSE

fft.inv(result, mulvec);

return result;