dolfin team mailing list archive

["Martin Sandve Alnæs" <martinal@xxxxxxxxx>]

UFC 1.1 already has a function for tabulating the number of dofs
associated with each mesh entity, but I don't think FFC implements UFC
1.1 completely yet. Shouldn't this be all that's needed from FFC for
DOLFIN to compute/estimate the max non-zeroes per row? Sum the local
dimension of all elements and subtract the number of dofs for each
entity shared by neighbouring elements.

--
Martin


2008/7/22 Garth N. Wells <gnw20@xxxxxxxxx>:
> I've been testing assembly with various back-ends, and the bottleneck is
> std::map::insert(..). I don't see an easy away around this which would
> yield the complete sparsity pattern.
>
> For various back-ends (PETSc, MTL4, and perhaps Trilinos), I would
> suggest that we go back to how we initialised matrices before the
> introduction of the sparsity pattern, where based on the number of
> neighbours to each cell and the finite element dimension, the maximum
> number of non-zeroes per row was estimated. With this information, there
> is no time overhead in assembling PETSc and MTL4 matrices relative to
> using the complete sparsity pattern.
>
> A more sophisticated but complex approach would be to allow FFC to help
> compute the maximum number of non-zeroes. How hard would it be for FFC
> to compute the maximum number of non-zeroes per row given the number of
> neighbours of a mesh entity? Using FFC, it would be possible to take
> into account the type of finite element.
>
> Garth
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