-------- Original Message -------- Subject: Re: [FEniCS] eval in parallel Date: 21/11/2014 12:22 From: Chris Richardson <ch...@bpi.cam.ac.uk> To: Mikael Mortensen <mikael.morten...@gmail.com> On 21/11/2014 11:52, Mikael Mortensen wrote:
On 20 Nov 2014, at 13:08, Jan Blechta <blec...@karlin.mff.cuni.cz> wrote:On Thu, 20 Nov 2014 11:33:26 +0100 Mikael Mortensen <mikael.morten...@gmail.com> wrote: On 20 Nov 2014, at 10:54, Chris Richardson <ch...@bpi.cam.ac.uk> wrote: There has been some discussion on bitbucket about how to best support evaluation and interpolation in parallel. At present, user code like this: mesh = UnitSquareMesh(10, 10) Q = FunctionSpace(mesh, "CG", 1) F = Function(Q) F.interpolate(Expression("x[0]")) print F(0.2, 0.2) crashes in parallel. e.g. with mpirun -n 2 *** Error: Unable to evaluate function at point. *** Reason: The point is not inside the domain. Consider setting "allow_extrapolation" to allow extrapolation. *** Where: This error was encountered inside Function.cpp. Clearly "allow_extrapolation" is not needed, and this is actually confusing to users. Agreed, allow_extrapolation is very confusing. It should not be thrown as an option, at least not in parallel.Please, do not remove it. allow_extrapolation is useful for circumventing failing floating-point-based evaluation of Cell::inside(Point& p) for p interior point near facet of the cell. The problem is covered here https://bitbucket.org/fenics-project/dolfin/issue/296 [2]. Floating point robustness should probably be handled inside the collision routines and not by flags in Function::eval. Nevertheless, it is very misleading to throw a suggestion to allow_extrapolation in parallel. I think we should add something like if (allow_extrapolation && MPI::size(_function_space->mesh()->mpi_comm()) == 1) or simply not allow setting allow_extrapolation to true in parallel. Chris, I think I’m leaning towards a brand new global_eval rather than modifying the existing eval. But I have no strong opinion on this.
Yes, I think there are reasonable fixes to Issue 296 (https://bitbucket.org/fenics-project/dolfin/issue/296/collision-algorithms-are-not-numerically) based on considering triangle edges, which should give consistent results on either side of a facet - but that is another issue.
I guess you might sometimes want to allow_extrapolation if a Point has strayed DOLFIN_EPS outside the original domain, e.g. refinement of an external edge.
-- Chris Richardson BP Institute Madingley Road Cambridge CB3 0EZ _______________________________________________ fenics mailing list fenics@fenicsproject.org http://fenicsproject.org/mailman/listinfo/fenics
