mat0  --  Simple matrix.
4 real
1 1  2.0
1 2 -1.0
2 1 -1.0
2 2  3.0
2 3 -1.0
3 2 -1.0
3 3  3.0
3 4 -1.0
4 3 -1.0
4 4  3.0
0 0  0.0
34.0
0.0
0.0
0.0