matrix 
Prompts for the row degrees to be assigned to this matrix. If <return> is typed, every row degree is set to zero. Otherwise, an integer list is expected. The system then prompts for the column degrees. If <return> is typed, the column degree of each non-zero column is computed from the above row degrees. Each column consisting entirely of zeros has its degree set to zero. If instead an integer list is given, this list is used as the column degrees. See section 3.7 for details on integer lists.
A warning message is displayed if the resulting matrix is not graded.