convolution_matrix.hpp

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#ifndef NIHU_CONVOLUTION_MATRIX_HPP_INCLUDED
#define NIHU_CONVOLUTION_MATRIX_HPP_INCLUDED
 
#include <Eigen/Dense>
 
#include <complex>
 
namespace NiHu
{
namespace fmm
{
 
template <class Scalar>
class convolution_matrix
{
public:
    typedef Scalar scalar_t;
    typedef Eigen::Matrix<scalar_t, Eigen::Dynamic, 1> vector_t;
 
    convolution_matrix()
    {
    }
 
    convolution_matrix(size_t N, size_t M, vector_t const &diag_coeffs)
        : m_N(N)
        , m_M(M)
        , m_diag_coeffs(diag_coeffs)
    {
    }
 
    vector_t operator *(vector_t const &rhs) const
    {
        if (rhs.rows() != Eigen::Index(2 * m_M + 1))
            throw std::runtime_error("Invalid input size in convolution matrix");
 
        vector_t res = vector_t::Zero(2 * m_N + 1, 1);
        int L = int((m_diag_coeffs.rows() - 1) / 2);
        // perform convolution by definition
        for (int n = -int(m_N); n <= int(m_N); ++n)
        {
            for (int m = -int(m_M); m <= int(m_M); ++m)
            {
                int c = n - m;
                if (c >= L || c <= -L)
                    continue;
                res(n + m_N) += m_diag_coeffs(c + L) * rhs(m + m_M);
            }
        }
        return res;
    }
 
private:
    size_t m_N;
    size_t m_M;
    vector_t m_diag_coeffs;
};
 
} // end of namespace fmm
} // end of namespace NiHu
 
#endif /* NIHU_CONVOLUTION_MATRIX_HPP_INCLUDED */