________________________________
From: Matthew Knepley <[email protected]>
Sent: Tuesday, April 17, 2018 8:38 AM
To: Young, Matthew, Adam
Cc: [email protected]
Subject: Re: [petsc-users] Reuse KSP
On Tue, Apr 17, 2018 at 8:33 AM, Young, Matthew, Adam
<[email protected]<mailto:[email protected]>> wrote:
My code (C/C++) uses PETSc to solve a linear system at each iteration in a
time-stepping scheme. The PETSc routines are separated out because the scheme
that uses them is optional in the larger code.
At each time step, the PETSc scheme calls a routine that includes:
{
Mat A;
Vec x,b;
KSP ksp;
[Set up A,x,b]
KSPCreate(PETSC_COMM_WORLD,&ksp);
[Build A and b from simulation data]
[Set nullspace of A with MatSetNullSpace]
KSPSetOperators(ksp,A,A);
KSPSetFromOptions(ksp);
KSPSolve(ksp,b,x);
[Write x into an instance of our array class, perform checks, etc.]
KSPDestroy(&ksp);
return(0);
}
My question is: If I want to use superLU_DIST with the option
-mat_superlu_dist_fact SamePattern (or SamePattern_SameRowPerm), should I move
KSPCreate/Destroy outside of the time-step loop in the larger code?
1) Yes
2) How are you using LU when A has a nullspace?
My bad - that code is in there from when I was trying iterative solvers. Should
I remove it if I use LU or will PETSc just ignore it?
3) You can also move out SetFromOptions().
Thanks for the advice. So, that means I'll build A and b from simulation data,
SetOperators(), Solve(), and carry on?
Matt
Thanks.
----------------------------
Matthew Young
PhD Candidate
Astronomy Department
Boston University
--
What most experimenters take for granted before they begin their experiments is
infinitely more interesting than any results to which their experiments lead.
-- Norbert Wiener
https://www.cse.buffalo.edu/~knepley/<http://www.caam.rice.edu/~mk51/>
