Hi, Rutger,

Thanks for your help. In my program, I want to access the entries of sparse matrix M as following:

typename ublas::compressed_matrix<double, ublas::row_major> ::iterator1 row; // Iterator over rows
typename ublas::compressed_matrix<double, ublas::row_major> ::iterator2 entry; // Iterator over entries
for (row = M.begin1();row != M.end1(); ++row) {
unit& i1 = row.index1(); // the row index

unit& j1 = row.index2(); // the column index for which one of the elements of M ? Is it the beginning element of row?

for (entry = row.begin(); entry != row.end(); ++entry) {

unit& i2 = entry.index1(); // the row index of element pointed by entry
unit& j2 = entry.index2(); // the column index of element pointed by entry

}
}

Best

Huayi