On Thu, Oct 18, 2012 at 2:28 PM, Matthew Knepley <knepley at gmail.com> wrote: > On Thu, Oct 18, 2012 at 11:07 AM, Nachiket Gokhale <gokhalen at gmail.com> > wrote: >> >> Hi, >> >> I am solving a Piezoelectric problem using Petsc. The structure is >> >> [ K_uu K_uv ] >> [K_uv ^T -K_v,v ] >> >> More details about the formulation: http://tinyurl.com/9hlbp4u >> >> K_uu has elements O(1E9) because the stiffnesses are in GPa, >> K_uv has elements O(1) because piezoelectric coefficients are of that >> order >> K_v,v has elements O(1E-9) because the dielectric constants are of >> that order. >> >> I am using Petsc, with pc_type LU and MUMPS for the factorization, >> -ksp_type gmres. I am not sure if my solution is converging. A typical >> solve seems to be doing this: >> >> 28 KSP preconditioned resid norm 5.642364260456e-06 true resid norm >> 1.228976487745e-03 ||r(i)||/||b|| 3.317409023627e-14 >> 29 KSP preconditioned resid norm 5.540718271043e-06 true resid norm >> 1.228453548651e-03 ||r(i)||/||b|| 3.315997440178e-14 >> 30 KSP preconditioned resid norm 1.973052106578e-03 true resid norm >> 1.220399172500e-03 ||r(i)||/||b|| 3.294256047735e-14 >> 31 KSP preconditioned resid norm 1.155762663956e-17 true resid norm >> 2.447631111938e-04 ||r(i)||/||b|| 6.606955965570e-15 >> >> Is there a right way to solve this set of equations? Is PCFieldSplit >> the recommended way? > > > First, you should really non-dimensionalize. You can see what this would > give > you by symmetrically scaling your problem with [ 3e4 3e-4 ], namely > everything > will be O(1). > > Second, you might get something out of using FieldSplit, but its tough to > tell > without knowing more about the operators. > > Matt > >> >> Thanks, >> >> -Nachiket >
Oh, right, thanks. I wasn't even thinking of it that way. I'll scale the variables and I'll give it a try. Cheers, -Nachiket > > > > -- > What most experimenters take for granted before they begin their experiments > is infinitely more interesting than any results to which their experiments > lead. > -- Norbert Wiener
