On 22/11/10 22:28, Johan Hake wrote: > On Saturday November 20 2010 10:02:36 Garth Wells wrote: >> I've done some testing, and using unordered_set appears to not perform >> as well as Set for standard problems. > > What are the differences in timing here?
I saw around a factor of 2. unordered_map also seems to use a lot more memory. > The difference in timing using > unordered_set for Real spaces where dramatically better. > >> 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. > > Is this true for any form? Why is this so notable when computing the sparsity > pattern when a subspace belongs to Real? > No, only forms with global dofs (like Real). >> 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. > > How would this help? > If we know that a dof is global, we can just insert it in the sparsity pattern for all cells. No need to perform a search (which is what get expensive for the 'Real' row, which is full). Garth > Johan > -- 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) _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : dolfin@lists.launchpad.net Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
