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

[Barry Smith]

> On Feb 23, 2015, at 5:18 AM, domenico lahaye <domenico_lahaye at yahoo.com> wrote:
> 
> Hi, 
> 
>   Contingency analysis of power systems requires to solve a sequence 
> a (non-)linear systems in which the Jacobian/matrix changes by a 
> rank-2/rank-1 update. 
> 
>    Does the PETSc interface to GAMG allow to freeze the AMG hierarchy 
> for a given matrix (base case) and to reuse this hierarchy in solving a list of 
> slightly perturbed linear problems (list of contingencies)? 

  You can do two things.

   Freeze the current preconditioner and solve a sequence of (new with slightly different numerical values) linear systems using that same precondition. Use KSPSetReusePreconditioner() in PETSc 3.5.x to freeze/unfreeze the preconditioner

   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.

   Barry
 
> 
>   Thanks, Domenico.