Barry,
Thank you so much. I'll try these options and see how they work.
Jiannan
From: Barry Smith
Sent: Tuesday, August 16, 2022 1:59 PM
To: Tu, Jiannan
Cc: petsc-users@mcs.anl.gov
Subject: Re: [petsc-users] Using matrix-free with KSP
CAUTION: This email was
MatMPIAIJSetPreallocation(A, 3, NULL, 0, NULL);
The 0 indicates you expect that there will be no matrix entries in the columns
of the matrix that represent degrees of freedom that are not stored on the
given rank. In your case this means you expect the matrix to be block diagonal
with one
Create another matrix B that contains "Selected parts of the matrix can be
pre-calculated and stored to serve as the preconditioner." When you call
KSPSetOperators() pass in B as the second matrix argument.
Now if literally application of B is the preconditioner you want to use,
then
I have managed to simplify my example program, and removed the
dependencies on slepc and gsl (attached).
The program defines a 800x800 matrix with 3 non-zero entries per row,
which are all set to 1.0.
When I run the program on 1 processor, everything works correctly. When
I run it on 2+
Your observed performance is explained by the number of iterations, which
varies based on a number of factors, plus imperfect memory bandwidth scaling
(https://petsc.org/release/faq/#what-kind-of-parallel-computers-or-clusters-are-needed-to-use-petsc-or-why-do-i-get-little-speedup).
Problems
Barry,
Thank you very much for your instructions. I am sorry I may not ask clearer
questions.
I don't use SNES. What I am trying to solve is a very large linear equation
system with dense and ill-conditioned matrix. Selected parts of the matrix can
be pre-calculated and stored to serve as the
Hello PETSc team,
I am currently using PETSc to improve the performance of a CFD solver by using
it's parallel linear solver. While doing so I ran across some scaling issues
where performance increase ( measured as KSPSolve time using MPI_Wtime()
function ) in the linear algebra operation was
I don't fully understand your question so I will answer questions that I do
know the answer to :-)
The function you provide to PCShellSetApply() applies the preconditioner to
the input vector and puts the result in the output vector. This input vector
changes at every application of the
I am trying to apply a user-defined preconditioner to speed up the convergency
of matrix-free KSP solver. The user's manual provides an example of how to call
the user-defined preconditioner routine. The routine has PC, input Vec and
output Vec as arguments. I want to use part of the Jacobian
