void Mesh::buildAreaMatrix(Eigen::SparseMatrix<double>& A) const
{
std::vector<Eigen::Triplet<double>> ATriplet;
for (VertexCIter v = vertices.begin(); v != vertices.end(); v++) {
ATriplet.push_back(Eigen::Triplet<double>(v->index, v->index, v->dualArea()));
}
A.setFromTriplets(ATriplet.begin(), ATriplet.end());
}
void Mesh::buildLaplacian(Eigen::SparseMatrix<double>& L) const
{
std::vector<Eigen::Triplet<double>> LTriplet;
for (VertexCIter v = vertices.begin(); v != vertices.end(); v++) {
HalfEdgeCIter he = v->he;
double dualArea = v->dualArea();
double sumCoefficients = 0.0;
do {
// (cotA + cotB) / 2A
double coefficient = 0.5 * (he->cotan() + he->flip->cotan()) / dualArea;
sumCoefficients += coefficient;
LTriplet.push_back(Eigen::Triplet<double>(v->index, he->flip->vertex->index, -coefficient));
he = he->flip->next;
} while (he != v->he);
LTriplet.push_back(Eigen::Triplet<double>(v->index, v->index, sumCoefficients));
}
L.setFromTriplets(LTriplet.begin(), LTriplet.end());
}