Function insert_from_triplets

deps/Eigen/src/SparseCore/SparseMatrix.h:1247–1260

// Creates a compressed sparse matrix from its existing entries and those from an unsorted range of triplets
template <typename InputIterator, typename SparseMatrixType, typename DupFunctor>
void insert_from_triplets(const InputIterator& begin, const InputIterator& end, SparseMatrixType& mat,
                          DupFunctor dup_func) {
  using Scalar = typename SparseMatrixType::Scalar;
  using SrcXprType =
      CwiseBinaryOp<scalar_disjunction_op<DupFunctor, Scalar>, const SparseMatrixType, const SparseMatrixType>;

  // set_from_triplets is necessary to sort the inner indices and remove the duplicate entries
  SparseMatrixType trips(mat.rows(), mat.cols());
  set_from_triplets(begin, end, trips, dup_func);

  SrcXprType src = mat.binaryExpr(trips, scalar_disjunction_op<DupFunctor, Scalar>(dup_func));
  // the sparse assignment procedure creates a temporary matrix and swaps the final result
  assign_sparse_to_sparse<SparseMatrixType, SrcXprType>(mat, src);
}

// Creates a compressed sparse matrix from its existing entries and those from an sorted range of triplets
template <typename InputIterator, typename SparseMatrixType, typename DupFunctor>