The rank of the Tutte matrix T of a graph G is equal to twice the size of a maximum matching of G.  There exists a nondeterministic algorithm based on this fact for maximum matching problem on a general graph G.  That is, repeatedly replace T's indeterminates with random real numbers and compute the rank of T, and let the size of maximum matching be the maximum rank / 2.  This works because the rank of T does not incrase by random assignments.

But the algorithm didn't work for me.  In particular, the graph with the adjacency matrix at the bottom of this code has a maximum matching of size 7, but the code reports it has 8.

What mistake did I make?