Hi, Sorry for small offtopic. I would also be interested more to know how it scales system? I mean what is idea behind this scaling.
Regards, Alexander On 23.12.2011 03:50, Mohamad M. Nasr-Azadani wrote: > Hi guys, > > Three questions: > 1) As mentioned on the web when we use > *-ksp_diagonal_scale_fix: *scale the matrix back AFTER the solve > > with -ksp_diagonal_scale does it also scale back the RHS vector > associated with the KSP solver? > > 2) Also, as mentioned on the web for -ksp_diagonal_scale > "Tells KSP > <http://www.mcs.anl.gov/petsc/petsc-3.1/docs/manualpages/KSP/KSP.html#KSP> to > symmetrically diagonally scale the system before solving. " > > When I used this option to solve for the Pressure (Poisson equation > with Neumann B.C., descritized via structured fisytenite-difference > method), the number of iterations for convergence was trippled, e.g. > without this option, it converges in 18 iteration, but with this > option it goes up to 50-60 iterations. > (GMRES + BoomerAMG as the preconditioner). > Is this something you would expect? > > 3) How could the linear system resulting from the Poisson equation for > pressure (incompressible flow) can be more diagonally scaled? To > elaborate more, for the uniform grid case and let's say a second order > central scheme finite difference discretization, the sum of the > off-diagonal coefficients are equal to the diagonal coefficient. > > Thanks, > Best, > Mohamad > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20111223/efb7d4c6/attachment.htm>
