MatrixUtils.hpp

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#pragma once
 
#include <polyfem/utils/Types.hpp>
 
#include <Eigen/Dense>
#include <Eigen/Sparse>
 
namespace polyfem
{
    namespace utils
    {
        // Show some stats about the matrix M: det, singular values, condition number, etc
        void show_matrix_stats(const Eigen::MatrixXd &M);
 
        template <typename T, int rows, int cols, int option, int maxRow, int maxCol>
        T determinant(const Eigen::Matrix<T, rows, cols, option, maxRow, maxCol> &mat)
        {
            assert(mat.rows() == mat.cols());
 
            if (mat.rows() == 1)
                return mat(0);
            else if (mat.rows() == 2)
                return mat(0, 0) * mat(1, 1) - mat(0, 1) * mat(1, 0);
            else if (mat.rows() == 3)
                return mat(0, 0) * (mat(1, 1) * mat(2, 2) - mat(1, 2) * mat(2, 1)) - mat(0, 1) * (mat(1, 0) * mat(2, 2) - mat(1, 2) * mat(2, 0)) + mat(0, 2) * (mat(1, 0) * mat(2, 1) - mat(1, 1) * mat(2, 0));
 
            assert(false);
            return T(0);
        }
 
        template <typename T>
        Eigen::Matrix<T, Eigen::Dynamic, Eigen::Dynamic, 0, 3, 3> inverse(const Eigen::Matrix<T, Eigen::Dynamic, Eigen::Dynamic, 0, 3, 3> &mat)
        {
            assert(mat.rows() == mat.cols());
 
            if (mat.rows() == 1)
            {
                Eigen::Matrix<T, 1, 1> inv;
                inv(0, 0) = T(1.) / mat(0);
 
                return inv;
            }
            else if (mat.rows() == 2)
            {
                Eigen::Matrix<T, 2, 2> inv;
                T det = determinant(mat);
                inv(0, 0) = mat(1, 1) / det;
                inv(0, 1) = -mat(0, 1) / det;
                inv(1, 0) = -mat(1, 0) / det;
                inv(1, 1) = mat(0, 0) / det;
 
                return inv;
            }
            else if (mat.rows() == 3)
            {
                Eigen::Matrix<T, 3, 3> inv;
                T det = determinant(mat);
                inv(0, 0) = (-mat(1, 2) * mat(2, 1) + mat(1, 1) * mat(2, 2)) / det;
                inv(0, 1) = (mat(0, 2) * mat(2, 1) - mat(0, 1) * mat(2, 2)) / det;
                inv(0, 2) = (-mat(0, 2) * mat(1, 1) + mat(0, 1) * mat(1, 2)) / det;
                inv(1, 0) = (mat(1, 2) * mat(2, 0) - mat(1, 0) * mat(2, 2)) / det;
                inv(1, 1) = (-mat(0, 2) * mat(2, 0) + mat(0, 0) * mat(2, 2)) / det;
                inv(1, 2) = (mat(0, 2) * mat(1, 0) - mat(0, 0) * mat(1, 2)) / det;
                inv(2, 0) = (-mat(1, 1) * mat(2, 0) + mat(1, 0) * mat(2, 1)) / det;
                inv(2, 1) = (mat(0, 1) * mat(2, 0) - mat(0, 0) * mat(2, 1)) / det;
                inv(2, 2) = (-mat(0, 1) * mat(1, 0) + mat(0, 0) * mat(1, 1)) / det;
 
                return inv;
            }
 
            assert(false);
            Eigen::Matrix<T, 1, 1> inv;
            inv(0, 0) = T(0);
            return inv;
        }
 
        inline Eigen::SparseMatrix<double> sparse_identity(int rows, int cols)
        {
            Eigen::SparseMatrix<double> I(rows, cols);
            I.setIdentity();
            return I;
        }
 
        Eigen::VectorXd flatten(const Eigen::MatrixXd &X);
 
        Eigen::MatrixXd unflatten(const Eigen::VectorXd &x, int dim);
 
        void vector2matrix(const Eigen::VectorXd &vec, Eigen::MatrixXd &mat);
 
        Eigen::SparseMatrix<double> lump_matrix(const Eigen::SparseMatrix<double> &M);
 
        void full_to_reduced_matrix(
            const int full_size,
            const int reduced_size,
            const std::vector<int> &removed_vars,
            const StiffnessMatrix &full,
            StiffnessMatrix &reduced);
 
        Eigen::MatrixXd reorder_matrix(
            const Eigen::MatrixXd &in,
            const Eigen::VectorXi &in_to_out,
            int out_blocks = -1,
            const int block_size = 1);
 
        Eigen::MatrixXd unreorder_matrix(
            const Eigen::MatrixXd &out,
            const Eigen::VectorXi &in_to_out,
            int in_blocks = -1,
            const int block_size = 1);
 
        Eigen::MatrixXi map_index_matrix(
            const Eigen::MatrixXi &in,
            const Eigen::VectorXi &index_mapping);
 
        template <typename DstMat, typename SrcMat>
        void append_rows(DstMat &dst, const SrcMat &src)
        {
            if (src.rows() == 0)
                return;
            if (dst.cols() == 0)
                dst.resize(dst.rows(), src.cols());
            assert(dst.cols() == src.cols());
            dst.conservativeResize(dst.rows() + src.rows(), dst.cols());
            dst.bottomRows(src.rows()) = src;
        }
 
        template <typename DstMat>
        void append_rows_of_zeros(DstMat &dst, const size_t n_zero_rows)
        {
            assert(dst.cols() > 0);
            if (n_zero_rows == 0)
                return;
            dst.conservativeResize(dst.rows() + n_zero_rows, dst.cols());
            dst.bottomRows(n_zero_rows).setZero();
        }
    } // namespace utils
} // namespace polyfem