message: code review: GUDHI_CHECK if u==v oninsert_edge method
diff: #define FLAG_COMPLEX_SPARSE_MATRIX_H_
  #include <gudhi/graph_simplicial_complex.h>
  +#include <gudhi/Debug_utils.h>
  #include <boost/functional/hash.hpp>
  #include <boost/graph/adjacency_list.hpp>
  @@ -264,11 +265,14 @@ class Flag_complex_sparse_matrix {
  }
  // Insert an edge in the data structure
  + // @exception std::invalid_argument In debug mode, if u == v
  void insert_new_edge(Vertex_handle u, Vertex_handle v, Filtration_value filt_val)
  {
  // The edge must not be added before, it should be a new edge.
  insert_vertex(u, filt_val);
  - if (u != v) {
  + GUDHI_CHECK((u != v),
  + std::invalid_argument("Flag_complex_sparse_matrix::insert_new_edge with u == v"));
  +
  insert_vertex(v, filt_val);
  #ifdef DEBUG_TRACES
  std::cout << "Insertion of the edge begins " << u <<", " << v << std::endl;
  @@ -282,12 +286,6 @@ class Flag_complex_sparse_matrix {
  sparse_row_adjacency_matrix_.insert(rw_u->second, rw_v->second) = filt_val;
  sparse_row_adjacency_matrix_.insert(rw_v->second, rw_u->second) = filt_val;
  }
  -#ifdef DEBUG_TRACES
  - else {
  - std::cout << "Already a member simplex, skipping..." << std::endl;
  - }
  -#endif // DEBUG_TRACES
  - }
  public:
  /** \brief Flag_complex_sparse_matrix constructor from a range of filtered edges.
  