On Fri, Mar 15, 2013 at 1:19 PM, Jens Lohne Eftang <[email protected]> wrote: > On 03/15/2013 03:16 PM, John Peterson wrote: >> >> On Fri, Mar 15, 2013 at 1:15 PM, John Peterson <[email protected]> >> wrote: >>> >>> On Fri, Mar 15, 2013 at 1:03 PM, Roy Stogner <[email protected]> >>> wrote: >>>> >>>> On Fri, 15 Mar 2013, Jens Lohne Eftang wrote: >>>> >>>>> On 03/15/2013 02:01 PM, Roy Stogner wrote: >>>>>> >>>>>> I'd start by turning on PETSc's monitor flags ('-ksp_monitor' etc?). >>>>>> Endless residual reevaluations suggests to me that the initial >>>>>> linear solve converged poorly and didn't give you a descent direction, >>>>>> and a subsequent line search is failing to find a reduced nonlinear >>>>>> residual. >>>>> >>>>> It seems to me that the residual gets assembled after the solver has >>>>> converged, for some reason. >>>> >>>> Yes: After you take a Newton step, the Newton solver typically wants >>>> to make sure that that step gave you a (nonlinear) residual reduction, >>>> and to see whether that new residual meets your tolerances so that the >>>> Newton iteration can claim convergence and exit. >>>> >>>> If you got a good linear solve (so the new proposed solution is a >>>> descent direction) but the next nonlinear residual is lousy, then >>>> typically the next operation is a line search, which does a whole >>>> bunch more residual evaluations at points in between the solution at >>>> the previous nonlinear solve and the failed proposed next step. >>>> >>>> But it looks like you're getting a good linear solve yet not getting a >>>> good line search result. Is it possible your residual and Jacobian >>>> aren't consistent? >>> >>> Petsc 3.3? You can also try "-snes_linesearch_type basic" to turn >>> linesearch off completely >>> >>> Prior to 3.3 it was "-snes_ls basic" >> >> Wait, nevermind, you said FEMSystem, which is base on ImplicitSystem, >> sorry. Those options won't do anything. > > Well, it did do something ... "-snes_linesearch_type basic" makes the solver > do multiple linear solves instead. That does not make any sense to me as I'm > just trying to solve Ax=b.
Well I think FEMSystem solves everything as though it were nonlinear. So if you make your ksp_rtol (linear tolerance) about the same as your nonlinear tolerance, the "nonlinear" solver should converge in 1 iteration. -- John ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_d2d_mar _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
