Ok, yes that makes it work in both cases. Thanks for taking a look at it. Dave
On Sep 2, 2013, at 1:54 AM, Martin Sandve Alnæs <[email protected]> wrote: > It's a bug in tensor representation. As a temporary fix, try setting: > parameters["form_compiler"]["representation"] = "quadrature" > at the top to disable tensor representation. > > Martin > > > > On 2 September 2013 10:26, Cotter, Colin J <[email protected]> > wrote: > Hi Dave, > This term can't be integrated exactly because it is not polynomial, so my > first guess would be that different quadrature rules are used for those two > different expressions (if you don't suggest a quadrature rule then FFC tries > to guess one from the expression). Try fixing the quadrature rule in that > term and see if the results are still different. > > all the best > --Colin > From: [email protected] [[email protected]] on > behalf of David Bernstein [[email protected]] > Sent: 01 September 2013 20:35 > To: [email protected] > Subject: [FEniCS] Question about nonlinear problem > > Hi Everyone, Recently I wrote a fenics python code for solving a nonlinear > advection diffusion equation which worked very well. However, I came across > one issue which I couldn't resolve and which is illustrated by the attached > code (simpler than original project but still seems to contain the problem). > > The example problem is identical to the one described here > > http://fenicsproject.org/documentation/tutorial/nonlinear.html > > except that the nonlinear term q(u) is (1-u)^(-2), i.e., the PDE is > > grad(grad(u)/(1-u)^2) = -f > > The attached code gives different results if q is written as "(1-u)**(-2)" > and "(1/(1-u))**2". Is there a reason for this? I would have thought they > should be equivalent. > > Thanks, > Dave > > _______________________________________________ > fenics mailing list > [email protected] > http://fenicsproject.org/mailman/listinfo/fenics > > _______________________________________________ > fenics mailing list > [email protected] > http://fenicsproject.org/mailman/listinfo/fenics > > > _______________________________________________ > fenics mailing list > [email protected] > http://fenicsproject.org/mailman/listinfo/fenics
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