Obtaining local sparsity pattern from form and/or *_integral
Obtaining local sparsity pattern from form and/or *_integral. The sparsity pattern of a form can be the combined sparsity patterns of the integrals, i.e. a worst-case-
/// Return the number of nonzeros in an element tensor
virtual uint num_nonzeros() const;
/// Return the number of nonzeros in an element tensor
virtual void tabulate_
// Explanation: Either we define (pattern[0][i], pattern[1][i])
// to hold the row and col of nonzero number i,
// or (pattern[i][0], pattern[i][1]). We could also use a single
// pointer uint*pattern, the choice depends on how it will be
// natural to use.
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JH:
This Blueprint might be outdated, but I think the ideas presented here can be useful for a Blueprint on reducing the memory footprint in the
GenericTensor
method in DOLFIN during assemble. See corresponding Blueprint in DOLFIN
https:/
The important here is to provide a way to know the dofs which are non zero in an integral.
/// Return the number of nonzeros in an element tensor for a given rank
virtual uint num_nonzeros(uint rank ) const;
/// Return the number of nonzeros in an element tensor for a given rank
virtual void tabulate_
These values can then be used to reduce the size of the tabulated tensor before
GenericTensor
is called. The cost of copying the values from a tabulated tensor (and from the dofmap) to a reduced version is much less than the extra time it takes to shuffle zeros around to the underlying linear algebra backend. This is a fairly non invasive way (nothing done to dof_map, or tabulate_tensor) of reducing the time spent in GenericTensor::add.
