When I work with sparse matrices, I prepare a list of row-column-value tuples, construct a COO<http://docs.scipy.org/doc/scipy/reference/generated/scipy.sparse.coo_matrix.html>matrix using that RCV data, then convert to CSR<http://docs.scipy.org/doc/scipy/reference/generated/scipy.sparse.csr_matrix.html>or CSC<http://docs.scipy.org/doc/scipy/reference/generated/scipy.sparse.csc_matrix.html>. I never modify a sparse matrix once built. It sounds like this may be a common approach per Christopher Mutel's message in the "sparse matrix construction question" thread from a few weeks ago. Cheers, Jason On Fri, Apr 20, 2012 at 3:07 PM, Duilio Tadeu <duiliotadeu@gmail.com> wrote:

Hi,

I am developing a simple Finite Elements code and there a part of the code where I need to set some elements of the sparse matrix (actually a submatrix), But I could not make it work. I have tried many ways.

I describe the better way I could try. The array index idx is 1x3, so idx1 and idx2 is 3x3. The (small) matrix M is 3x3. The matrix A is a sparse matrix, lil_matrix sparse matrix of scipy.sparse

###### partial code ##################

M = local_matrix(x,y) M=M.ravel()

idx1,idx2 = numpy.meshgrid(idx,idx) idx1=idx1.ravel() idx2=idx2.ravel()

A[idx1,idx2] = A[idx1,idx2] + M

###################################

In fact, I am trying to migrate from MATLAB to Scipy/Numpy, but this part is taking some time and is becoming frustrating, since I could not find any kind of way to perform this task. In MATLAB, the code would be just:

M = local_matrix(x,y) A[idx,idx] = A[idx,idx] + M

Which is shorter and easy. I send next the error message. Any help is welcome. Thanks, Duilio

131 idx2=idx2.ravel() 132 --> 133 A[idx1,idx2] = A[idx1,idx2] + M

/usr/lib/python2.6/dist-packages/scipy/sparse/lil.pyc in __setitem__(self, index, x) 318 else: 319 for ii, jj, xx in zip(i, j, x): --> 320 self._insertat(ii, jj, xx) 321 elif isinstance(i, slice) or issequence(i): 322 rows = self.rows[i]

/usr/lib/python2.6/dist-packages/scipy/sparse/lil.pyc in _insertat(self, i, j, x) 230 row = self.rows[i] 231 data = self.data[i] --> 232 self._insertat2(row, data, j, x) 233 234 def _insertat2(self, row, data, j, x):

/usr/lib/python2.6/dist-packages/scipy/sparse/lil.pyc in _insertat2(self, row, data, j, x) 244 245 if not np.isscalar(x): --> 246 raise ValueError('setting an array element with a sequence') 247 248 try:

ValueError: setting an array element with a sequence _______________________________________________ SciPy-User mailing list SciPy-User@scipy.org http://mail.scipy.org/mailman/listinfo/scipy-user

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