On 23 March 2011 22:05, Peter Brune <[email protected]> wrote: > I saw this thread and had already started running the tests I had for this > with the latest FFC to see if anything had changed recently. I never made > isoparametry through UFL public because I could never get the efficiency to > be reasonable. The situation appears to have improved a little bit from a > year ago, but not much. With the latest FFC, it's about 10x slower (in 2D) > to assemble Poisson with P1 for the test/trial space and P2 for the > coordinates than the same problem with affine coordinates. It's even worse > if you include things like Piola-transformed surface normals into the mix. > When I was working on this I only assembled a very small fraction of the > elements (around a cylinder in a flow) with the parametric Jacobian, so it > worked OK for small problems. > > I believe that it would do much, much better if the optimizing quadrature > compiler in FFC supported fractions. This is necessary because you need to > apply the inverse isoparametric Jacobian, which includes 1 / |J|, to any > basis function derivatives in the form.
It does support fractions, but maybe I don't quite follow your objection. It's difficult to give pointers when the code in question is secret.... Kristian > For reference, here are the assembly times for the iso(super, I suppose is > more accurate)-parametric, optimized, and non-optimized Poisson problems in > 2D on a 256x256 square (with the parametric coordinates just being the > regular coordinates passed through). > > isoparametric assembly | 3.2017 3.2017 1 > optimized assembly | 0.34515 0.34515 1 > regular assembly | 0.36524 0.36524 1 > > I got really deep in FFC trying to make this work with no success, but this > was before the rewrite. I'd be willing to declare victory on this one and > submit my code if someone else were willing to make it fast enough to use. > There's also the issue of how exactly to extend the interface to support > this in an elegant fashion. Right now I just call a function that takes a > form and a parametric Jacobian, runs a Transformer on the form, and spits > out a new form. > > - Peter > > > On Wed, Mar 23, 2011 at 3:30 PM, Anders Logg <[email protected]> wrote: >> >> Peter Brune claims to have solved this by a small addition to the form >> language that automatically expresses the curved elements as a mapping >> and expands appropriately (and invisible to the user) those mappings >> to yield a form that may then be assembled. The higher order geometry >> is then expressed as a vector-field on the mesh. >> >> Perhaps Peter can be pushed to polish up on his code and submit it. >> >> -- >> Anders >> >> >> On Wed, Mar 23, 2011 at 07:46:57PM +0000, Garth N. Wells wrote: >> > We haven't really looked at this. It was discussed a while back, but no >> > one has committed much time to it. We struggled to settle on an >> > appropriate abstraction to push on with. >> > >> > Garth >> > >> > On 23/03/11 18:40, Douglas Arnold wrote: >> > > What is the status of curved (e.g., isoparametric) elements in dolfin? >> > > I gather they are not implemented in the main branch. Has anyone >> > > done anything with this can be used? Is there any example code? >> > > (For example, if you want to >> > > solve the Poisson problem in a disc and get better than 2nd order >> > > convergence, you need to do better than polygonal approximation of >> > > the disc.) >> > > >> > > -- Doug >> > > >> > > _______________________________________________ >> > > Mailing list: https://launchpad.net/~dolfin >> > > Post to : [email protected] >> > > Unsubscribe : https://launchpad.net/~dolfin >> > > More help : https://help.launchpad.net/ListHelp >> > >> > _______________________________________________ >> > Mailing list: https://launchpad.net/~dolfin >> > Post to : [email protected] >> > Unsubscribe : https://launchpad.net/~dolfin >> > More help : https://help.launchpad.net/ListHelp >> > > > _______________________________________________ > Mailing list: https://launchpad.net/~dolfin > Post to : [email protected] > Unsubscribe : https://launchpad.net/~dolfin > More help : https://help.launchpad.net/ListHelp > > _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
