On Wed, Mar 30, 2016 at 7:47 AM, Paul T. Bauman <ptbau...@gmail.com> wrote:
> Hey David, > > On Tue, Mar 29, 2016 at 10:43 PM, David Knezevic < > david.kneze...@akselos.com> wrote: > >> I'm using FEMSystem for a problem, and I'm getting solid quadratic >> convergence with the Newton solver. However, when I turn on the finite >> difference jacobian check using "verify_analytic_jacobians = 1.e-6" it >> reports an error: >> "Relative error 0.133922 detected in analytic jacobian on element 0!" >> > > There are circumstances where I get this behavior, that is quadratic > convergence and the Jacobian is (partially) wrong. The one that pops to > mind is my Rayleigh-damping implementation, where I haven't yet implemented > parts of the Jacobian. (Just to satisfy any curiosity, for material > nonlinearities, C(i,j,k,l) has non-zero derivatives w.r.t. strain, so I > haven't yet gone to the trouble to implement them, but I have the Jacobian > for all the other parts.) > > >> I expected the code to pass this test, given that I'm getting good >> convergence behavior. So before I do too much more bug-hunting, I just >> wanted to check if there's a chance that I might be getting a "false >> positive" with the finite difference jacobian check? >> > > I have yet to find a case where I got a false positive. I find it helpful > to get to a very small problem and compare the elements to zone in on the > terms that differ. > Thanks for your comments. The problem I'm considering is plasticity, using the radial return algorithm. As far as I can tell, the code matches the text book, and it converges correctly. However, it doesn't match the finite difference Jacobian from FEMSystem. So there are two possibilities: 1) Somehow the finite difference Jacobian is inconsistent with the radial return algorithm. This doesn't seem impossible to me, given that the radial return algorithm is highly path-dependent. 2) There is a bug somewhere in my analytical Jacobian. I'll look some more for a bug (I'll compare the elements, like you said). But I was wondering if you think 1) is a possibility? David ------------------------------------------------------------------------------ Transform Data into Opportunity. Accelerate data analysis in your applications with Intel Data Analytics Acceleration Library. Click to learn more. http://pubads.g.doubleclick.net/gampad/clk?id=278785471&iu=/4140 _______________________________________________ Libmesh-users mailing list Libmesh-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libmesh-users
