libigl_Martin/include/igl/cotmatrix.cpp

#include "cotmatrix.h"

// For error printing
#include <cstdio>
#include "cotangent.h"

template <typename DerivedV, typename DerivedF, typename Scalar>
IGL_INLINE void igl::cotmatrix(
  const Eigen::MatrixBase<DerivedV> & V, 
  const Eigen::MatrixBase<DerivedF> & F, 
  Eigen::SparseMatrix<Scalar>& L)
{
  using namespace igl;
  using namespace Eigen;

  DynamicSparseMatrix<Scalar, RowMajor> dyn_L (V.rows(), V.rows());
  Matrix<int,Dynamic,2> edges;
  int simplex_size = F.cols();
  // 3 for triangles, 4 for tets
  assert(simplex_size == 3 || simplex_size == 4);
  if(simplex_size == 3)
  {
    // This is important! it could decrease the comptuation time by a factor of 2
    // Laplacian for a closed 2d manifold mesh will have on average 7 entries per
    // row
    dyn_L.reserve(7*V.rows());
    edges.resize(3,2);
    edges << 
      1,2,
      2,0,
      0,1;
  }else if(simplex_size == 4)
  {
    dyn_L.reserve(17*V.rows());
    edges.resize(6,2);
    edges << 
      1,2,
      2,0,
      0,1,
      3,0,
      3,1,
      3,2;
  }else
  {
    return;
  }
  // Gather cotangents
  Matrix<Scalar,Dynamic,Dynamic> C;
  cotangent(V,F,C);
  
  // Loop over triangles
  for(int i = 0; i < F.rows(); i++)
  {
    // loop over edges of element
    for(int e = 0;e<edges.rows();e++)
    {
      int source = F(i,edges(e,0));
      int dest = F(i,edges(e,1));
      dyn_L.coeffRef(source,dest) += C(i,e);
      dyn_L.coeffRef(dest,source) += C(i,e);
      dyn_L.coeffRef(source,source) += -C(i,e);
      dyn_L.coeffRef(dest,dest) += -C(i,e);
    }
  }
    // Corner indices of this triangle
  L = SparseMatrix<Scalar>(dyn_L);
}

#ifndef IGL_HEADER_ONLY
// Explicit template specialization
// generated by autoexplicit.sh
template void igl::cotmatrix<Eigen::Matrix<double, -1, -1, 0, -1, -1>, Eigen::Matrix<int, -1, -1, 0, -1, -1>, double>(Eigen::MatrixBase<Eigen::Matrix<double, -1, -1, 0, -1, -1> > const&, Eigen::MatrixBase<Eigen::Matrix<int, -1, -1, 0, -1, -1> > const&, Eigen::SparseMatrix<double, 0, int>&);
#endif