[petsc-users] Solving multiple linear systems with similar matrix sequentially

[Barry Smith]

> On Feb 23, 2015, at 9:41 PM, Jed Brown <jed at jedbrown.org> wrote:
> 
> Barry Smith <bsmith at mcs.anl.gov> writes:
>>   Freeze the hierarchy and coarse grid interpolations of GAMG but
>>   compute the new coarse grid operators RAP for each new linear
>>   system (this is a much cheaper operation). Use
>>   PCGAMGSetReuseInterpolation() to freeze/unfreeze the hierarchy.
> 
> The RAP is often more than 50% of PCSetUp, so this might not save much.

   Hee,hee  in some of my recent runs of GAMG the RAP was less than 25% of the time. Thus skipping the other portions could really pay off.*

  Barry

* this could just be because the RAP portion has been optimized much more than the other parts but ...