Do not assemble zero contributions from local to global matrix #543
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Codecov ReportBase: 92.93% // Head: 92.98% // Increases project coverage by
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With this patch, entries from the local matrix that are zero are ignored and never added to the global matrix. More importantly, it is now allowed to have missing stored entries in the global matrix if the contribution that would have been added there is zero. A concrete example where this is useful: Consider a two-field problem with unknowns (u, p) and test functions (v, q) where there is no coupling between, for example, p and q. In the global block matrix K = [A B; C D], D will be zero, and there is therefore no need to allocate entries in K corresponding to all couplings between p- and q-dofs. (Note though that currently it is not possible to create such a sparsity pattern because create_sparsity_pattern assumes full coupling between fields.) However, when assembling the local matrix k = [a b; c d] it is much easier to use a dense matrix, and simply initialize d to zero. After this patch it is perfectly fine to assemble the matrix k into K, even if the global entries for d are missing.
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With this patch, entries from the local matrix that are zero are ignored and never added to the global matrix. More importantly, it is now allowed to have missing stored entries in the global matrix if the contribution that would have been added there is zero.
A concrete example where this is useful: Consider a two-field problem with unknowns (u, p) and test functions (v, q) where there is no coupling between, for example, p and q. In the global block matrix K = [A B; C D], D will be zero, and there is therefore no need to allocate entries in K corresponding to all couplings between p- and q-dofs. (Note though that currently it is not possible to create such a sparsity pattern because create_sparsity_pattern assumes full coupling between fields.) However, when assembling the local matrix k = [a b; c d] it is much easier to use a dense matrix, and simply initialize d to zero. After this patch it is perfectly fine to assemble the matrix k into K, even if the global entries for d are missing.
Extracted from #539.