[petsc-users] How to decompose and record a constant A

[Dave May]

On Tue, 9 Apr 2019 at 10:33, Mark Adams via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> PETSc solvers will cache any setup computations, like a matrix
> factorization, and will reuse them on subsequent solves.
>
> If you call KSPSetOperators, PETSc will assume its cache is invalid and
> redo any required setup on subsequent solves.
>

Following from what Mark said, if you want an exact solve, use -pc_type lu.
Note that this will not store the inverse, rather only the L, U factors.
During setup, the L,U factors are created and subsequent solves will simply
apply the forward and backward solves using these factors.



> Mark
>
> On Tue, Apr 9, 2019 at 4:08 AM ztdepyahoo via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
>
>> Dear group:
>>       I need to solve a Laplacian problem Ax=b every time step where A is
>> a constant . I want to store the inverse of A at the first time step.
>> how to do with Petsc
>>  Regards
>>
>> ztdepyahoo
>> ztdepyahoo at gmail.com
>>
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>
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