On Sun, Apr 29, 2007 at 12:02:59PM +0200, Garth N. Wells wrote:
Garth N. Wells wrote:
Anders Logg wrote:
On Fri, Apr 27, 2007 at 05:24:34PM +0200, Garth N. Wells wrote:
Anders Logg wrote:
I'm comparing the entries in the Stokes systems between the new code
and the old and there seem to be quite a few more zeros in the sparse
matrix than before.
Strange. Have you counted the non-zeroes, or are you displaying the
matrix?
Displaying the matrix and counting everything that looks like zero.
(Just looking at the numbers.)
There are about double the number of non-zeros (you can get the number
by A.nnz()) for the Stokes example with the new version compared to
version 0.6.4. For poisson and elasticity, the number of non-zeroes is
the same as with version 0.6.4. The linear algebra looks fine -
something is going on with the computation of the sparsity pattern for
the Stokes problem.
This is due to the significant number of zeroes in the element matrix
for the Stokes problem. Previously, for uBLAS matrices the stiffness
matrix was assembled into a temporary matrix A_temp which was then
copied to a compressed row matrix A
A.assign(A_temp);
The assign operation removed all non-zero terms. We no longer assemble
into the temporary matrix.
Perhaps FFC could produce something to indicate the non-zero terms in
the element matrix, although this would make things more complicated.
Garth
We could add something like
void tabulate_nonzero_entries(bool* nonzero_entries);
to go along with tabulate_tensor() in the UFC interface.
