On 03/15/2013 04:09 PM, Roy Stogner wrote: > > On Fri, 15 Mar 2013, Jens Lohne Eftang wrote: > >> But when the residual is computed how can I hand it just "b," ? I >> thought it would calculate it as A*x-b based on my A and b ...? > > Nope. As John said, FEMSystem doesn't have any way to tell whether > your problem is linear or not. If you've got a linear problem, then > it's up to you to tell the nonlinear solver to avoid doing any > redundant work, and if you want it to be robust with any solver (or > with time integration) then it's up to you to define a > solution-dependent residual consistently. > > Usually this isn't too hard - E.g. if I was solving > > (grad u, grad v) = (f, v) > > Then my residual is (f,v)-(grad u, grad v) instead of plain (f,v). > > If you know you're never going to evaluate your problem from a > starting point other than u=0, then you can get away with plain (f,v) > as long as you turn off any nonlinear solver option that might call a > residual after the first step. But usually people intend to do > nonlinear or transient terms eventually too, so it's easier to just > start with the linear terms written in a consistent way.
Got it! Thanks guys! Jens > --- > Roy ------------------------------------------------------------------------------ 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
