dolfin team mailing list archive

[Martin Sandve Alnæs <martin.alnes@xxxxxxxxx>]

I haven't looked at the code, but just some general STL advice:
- Never use std::find on map and set types in stl, use their member
function find instead. std::find could be a linear search in this
case...
- Don't use the [] operator to read elements from maps and sets, use
mymap.find instead.

Martin



2010/11/20 Garth Wells <668862@xxxxxxxxxxxxxxxxxx>:
> I've done some testing, and using unordered_set appears to not perform
> as well as Set for standard problems.
>
> Each dof (matrix row) has its own set. The sets are usually small, and
> independent of the mesh size. The problem is that the size of set that
> belongs to the global dof is equal to the number of columns in the
> matrix, and when looping over this set (which becomes very large)
> std::find is called a lot.
>
> I don't see simple solution from the SparsityPattern side. What's
> probably needed is an extension to UFC to distinguish between local and
> global dofs.
>
> --
> Sparsity pattern computation dead slow with 'real' spaces
> https://bugs.launchpad.net/bugs/668862
> You received this bug notification because you are a member of DOLFIN
> Team, which is subscribed to DOLFIN.
>
> Status in DOLFIN: Confirmed
>
> Bug description:
> The computation of the sparsity pattern is dead slow when real spaces are used, i.e.,
>
>    R = FunctionSpace(mesh, 'R', 0)
>
> To see the problem, compare the neumann-poisson and poisson demos with fine meshes (256x256)
>
>
>
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