Hi Barry, The linear solvers converge in 1 iterations. But the SNES solver fails when I use the direct solver. Thanks,Subramanya
> Subject: Re: [petsc-users] Behaviour of Newton Methods with Direct Solvers. > From: [email protected] > Date: Fri, 30 Aug 2013 21:11:36 -0500 > CC: [email protected] > To: [email protected] > > > I would not expect this. Are you sure that direct solvers are actually > working well? You can run -ksp_type gmres -pc_type lu to "accelerate" the > direct solver. Under normal circumstances the direct solver will converge in > one iteration but if, for example, the problem is singular or nearly singular > several iterations might solve the linear system but one may not. > > Barry > > On Aug 30, 2013, at 9:08 PM, subramanya sadasiva <[email protected]> wrote: > > > Hi, > > Is there a reason that the convergence of the newton methods in SNES is > > much better with iterative solvers instead of with direct solvers? This is > > particularly in reference with the VI solvers. I get nearly quadratic > > convergence with the iterative solvers, but the code just diverges or > > converges linearly when i run with -ksp_type preonly . > > Thanks, > > Subramanya >
