# whenever we come across an index pair `$(i,j)$` with
# `$A_{ij} = 0$`.
spanning_set = []
- for j in range(0, A.ncols()):
- for i in range(0,j):
+ for j in xrange(A.ncols()):
+ for i in xrange(j):
if A[i,j] == 0:
M = A.matrix_space()
S = X.transpose() * (stdE(M,i,j) + stdE(M,j,i)) * X