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