[SciPy-user] multiplying sparse matrices in scipy-0.4.8?

afraser afraser at lanl.gov
Thu Mar 23 11:09:16 CST 2006

I'm using numpy-0.9.6 and scipy-0.4.8.  When I multiply sparse
matrices, I often get the error: "ValueError: nzmax must not be less
than nnz".  The error happens when the matrices are only sort of
sparse.  Any advice appreciated.

Here is a sample program and Traceback:
import numpy, scipy, scipy.sparse, random

L = 30
frac = .3

random.seed(0) # make runs repeatable
A = scipy.sparse.csc_matrix((L,2))
#A = numpy.asmatrix(numpy.zeros((L,2),numpy.Float))

for i in xrange(L):
    for j in xrange(2):
        r = random.random()
        if r < frac:
            A[i,j] = r/frac
B = A*A.T
print B
Traceback (most recent call last):
  File "<stdin>", line 15, in ?
  File "/usr/lib/python2.3/site-packages/scipy/sparse/sparse.py", line 658, in __mul__
    return self.dot(other)
  File "/usr/lib/python2.3/site-packages/scipy/sparse/sparse.py", line 306, in dot
    result = self.matmat(other)
  File "/usr/lib/python2.3/site-packages/scipy/sparse/sparse.py", line 824, in matmat
    return csc_matrix((c, rowc, ptrc), dims=(M, N))
  File "/usr/lib/python2.3/site-packages/scipy/sparse/sparse.py", line 558, in __init__
  File "/usr/lib/python2.3/site-packages/scipy/sparse/sparse.py", line 574, in _check
    raise ValueError, "nzmax must not be less than nnz"
ValueError: nzmax must not be less than nnz


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