[petsc-users] Enquiry regarding log summary results

[TAY wee-beng]

On 6/10/2012 11:42 PM, Jed Brown wrote:
> On Sat, Oct 6, 2012 at 4:19 PM, TAY wee-beng <zonexo at gmail.com 
> <mailto:zonexo at gmail.com>> wrote:
>
>     May I know where can I find all the options for GAMG? I can't find
>     it in the manual.
>
>
> As always, run with -help. The options for GAMG specifically are 
> controlled under the prefix -pc_gamg_*. The smoothers  and coarse grid 
> solvers are configured under -mg_levels_*.
>
>
>     I also used -info for the GAMG and what does these mean:
>
>     1. [9] MatAssemblyBegin_MPIAIJ(): Stash has 14396 entries, uses 1
>     mallocs
>
>
>     How serious is this? Does it mean there's a lot of mallocs going
>     on? Do I correct this by using higher d_nz and o_nz?
>
>
> No, the stash holds entries that are stored on a different process 
> from where you assemble. Assembling some values off-process is common 
> for finite element discretizations, for example. Less than one percent 
> of the values are assembled off-process, which is fine.
>
>
>     2. [4] MatAssemblyEnd_SeqAIJ(): Matrix size: 112785 X 112785;
>     storage space: 0 unneeded,3628127 used
>     [4] MatAssemblyEnd_SeqAIJ(): Number of mallocs during
>     MatSetValues() is 0
>     [4] MatAssemblyEnd_SeqAIJ(): Maximum nonzeros in any row is 59
>
>     When I use MatCreateAIJ, my d_nz and o_nz are both 7. If the row
>     is 59, does it mean that my d_nz and o_nz are too small. Must I
>     set it to the maximum nonzeros given by -info?
>
>
> Either this line is not the first assembly or you didn't pass 7. If 
> you don't want to use extra memory, you should preallocate exactly, 
> otherwise it is better to over-estimate than to under-estimate.
This line happens rather late in the assembly, so it is not the main 
matrix which I've created, right? And hence this doesn't matter?
>
>
>     3. [0] MatSetOption_SeqAIJ(): Option STRUCTURALLY_SYMMETRIC ignored
>
>     My Poisson matrix is symmetrical, so why is it ignored?
>
>
> This is a bad info message. That option is handled at a higher level. 
> I'll fix it.

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