Re: [petsc-users] GAMG advice

2017-10-20 Thread Barry Smith
David, GAMG picks the number of levels based on how the coarsening process etc proceeds. You cannot hardwire it to a particular value. You can run with -info to get more info potentially on the decisions GAMG is making. Barry > On Oct 20, 2017, at 2:06 PM, David Nolte

Re: [petsc-users] "Must select a target sorting criterion if using shift-and-invert"

2017-10-20 Thread Matthew Knepley
On Fri, Oct 20, 2017 at 7:43 PM, Kong, Fande wrote: > Hi All, > > I am trying to solve a generalized eigenvalue problem (using SLEPc) with > "-eps_type krylovschur -st_type sinvert". I got an error message: "Must > select a target sorting criterion if using shift-and-invert".

[petsc-users] "Must select a target sorting criterion if using shift-and-invert"

2017-10-20 Thread Kong, Fande
Hi All, I am trying to solve a generalized eigenvalue problem (using SLEPc) with "-eps_type krylovschur -st_type sinvert". I got an error message: "Must select a target sorting criterion if using shift-and-invert". Not sure how to proceed. I do not quite understand this sentence. Fande,

Re: [petsc-users] Distributing already assembled stiffness matrix

2017-10-20 Thread Mark Adams
On Fri, Oct 20, 2017 at 6:42 PM, Barry Smith wrote: > > > On Oct 18, 2017, at 4:14 AM, Jaganathan, Srikrishna < > srikrishna.jaganat...@fau.de> wrote: > > > > Hello, > > > > > > I have been trying to distribute a already existing stiffness matrix in > my FEM code to petsc

Re: [petsc-users] Distributing already assembled stiffness matrix

2017-10-20 Thread Barry Smith
> On Oct 18, 2017, at 4:14 AM, Jaganathan, Srikrishna > wrote: > > Hello, > > > I have been trying to distribute a already existing stiffness matrix in my > FEM code to petsc parallel matrix object , but I am unable to find any > documentation regarding it.

Re: [petsc-users] GAMG advice

2017-10-20 Thread David Nolte
PS: I didn't realize at first, it looks as if the -pc_mg_levels 3 option was not taken into account:   type: gamg     MG: type is MULTIPLICATIVE, levels=1 cycles=v On 10/20/2017 03:32 PM, David Nolte wrote: > Dear all, > > I have some problems using GAMG as a preconditioner for (F)GMRES. >

[petsc-users] GAMG advice

2017-10-20 Thread David Nolte
Dear all, I have some problems using GAMG as a preconditioner for (F)GMRES. Background: I am solving the incompressible, unsteady Navier-Stokes equations with a coupled mixed FEM approach, using P1/P1 elements for velocity and pressure on an unstructured tetrahedron mesh with about 2mio DOFs (and

Re: [petsc-users] Good performance For small problem on GALILEO

2017-10-20 Thread Matthew Knepley
Justin is right that parallelism will be of limited value for such small systems. This looks like a serial optimization job. Moreover, in this case, a better numerical method usually trumps any kind of machine optimization. Matt On Fri, Oct 20, 2017 at 2:55 AM, Justin Chang

Re: [petsc-users] Good performance For small problem on GALILEO

2017-10-20 Thread Justin Chang
600 unknowns is way too small to parallelize. Need at least 10,000 unknowns per MPI process: https://www.mcs.anl.gov/petsc/documentation/faq.html#slowerparallel What problem are you solving? Sounds like you either compiled PETSc with debugging mode on or you just have a really terrible solver.