Starting new matrix.
mna1  --  Simple modified node admittance matrix.
4
1 1  2.0
1 2 -2.0
2 1 -2.0
2 2  2.0
1 3  1.0
2 4  1.0
3 1  1.0
4 2  1.0
0 0  0.0
Beginning source vector.
0.0
0.0
1.0
-1.0