Method is_end_iterator

source/matplot/util/common.h:642–645

                return it._vec == nullptr;
            }
            static bool is_end_iterator(const iterator &it) {
                return is_empty_iterator(it) ||
                       it._row_offset * it._col_offset >= it._vec->size();
            }

          public:
            iterator(vector_2d_view *const vec)