On Mon, Aug 8, 2016 at 10:06 PM, Roy Stogner <royst...@ices.utexas.edu> wrote:
> > On Mon, 8 Aug 2016, Vikram Garg wrote: > > We have a domain split up into two subdomains, the first subdomain >> has a higher resolution mesh and solves a complex physics, while the >> second >> has a lower resolution mesh and a simpler physics. >> > > Same variables but with different weak residuals? > > Yes. The simpler residual has pure diffusion, while complex one has an additional convection and reaction term (and hence finer mesh). > We are observing that, with GMRES, >> > > Linear problem in both physics? Nope, the reaction makes the complex physics nonlinear. > > > the completely complex problem solves much faster >> > > Fewer iterations? Wall clock time is a lot harder to pin down. > Yup. Fully complex takes 6 NL iterations, and 132 total linear steps. Whereas, 10% complex also takes 6 NL steps (which is again a bit surprising) and 208 total linear steps. > > What preconditioner are you currently using? > > -ksp_gmres_modifiedgramschmidt -ksp_gmres_restart 500 -pc_type ilu -pc_factor_levels 4 -pc_factor_shift_type nonzero > than with a multiphysics setup (10% domain being complex physics). >> > > How fast does it solve with 0% domain being complex physics? > > 2 NL iterations, and 24 total linear solver steps. > We are trying to see if this is due to a linear solver choice >> issue. >> >> Would GMRES have a problem with a subdomain physics/mesh split up ? >> > > I'm wondering if rather your physics is more "complex" in terms of > residual evaluation but is easier on the solver somehow. > Thats a tempting direction for an explanation. But think about this way, if we used LU, then if both the 10% and full complex take the same number of NL steps, the 10% will be far cheaper, because of a lower dof count. The efficacy of GMRES depends on the spectra, and we did do some investigation of the condition numbers of the matrices we were solving. Dont recall the precise findings, but I dont remember them being wildly different (Harriet can you confirm/add ?). Is PCFIELDSPLIT a better way to go here ? >> > > libMesh makes fieldsplits between different variables easy enough now, > but I don't think we've added any options to make field splits between > subdomains easy, so I think you'll need to code the PETSc index sets > yourselves to do this. > Any idea how difficult this will be ? > --- > Roy > -- Vikram Garg Postdoctoral Associate The University of Texas at Austin http://vikramvgarg.wordpress.com/ http://www.runforindia.org/runners/vikramg ------------------------------------------------------------------------------ What NetFlow Analyzer can do for you? Monitors network bandwidth and traffic patterns at an interface-level. Reveals which users, apps, and protocols are consuming the most bandwidth. Provides multi-vendor support for NetFlow, J-Flow, sFlow and other flows. Make informed decisions using capacity planning reports. http://sdm.link/zohodev2dev _______________________________________________ Libmesh-users mailing list Libmesh-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libmesh-users
