[Trilinos-Users] [EXTERNAL] Belos::LinearProblem::setProblem() is taking too much time

[Bradley, Andrew Michael]

Hi John,


1. What is your preconditioner? Is your preconditioner doing anything different on the first call compared with subsequent calls? It is called once in setProblem, I believe.


2. Solve time is shown as 42 seconds. Is that for 400 iterations, or is 400 the iteration limit? If it's the limit, how many iterations are actually performed?


Cheers,

Andrew


________________________________
From: trilinos-users-bounces at software.sandia.gov <trilinos-users-bounces at software.sandia.gov> on behalf of John Moore <johnpmooreiv at gmail.com>
Sent: Monday, February 16, 2015 12:10 PM
To: trilinos-users at software.sandia.gov
Subject: [EXTERNAL] [Trilinos-Users] Belos::LinearProblem::setProblem() is taking too much time

I am interested in solving large linear systems within Newton iterations. My matrix structure remains constant, while only the values change.

I find that most of the time is actually spent in the functions Belos::LinearProblem::setProblem. Is this to be expected? The case that I am currently running is detailed below:

TpetraCrsMatrix
# processors:        32 mpi processes
Number of rows:   802225
Number of entries:  71819925
Preconditioner:       Custom
Number of iters:     400
Solve time:            42 Seconds
setProblem time:     35 seconds

The performance only gets work as the problem gets larger.  For a slightly larger (and denser) problem, the setProblem() time is about 4 times that of the solve time. For small problems, most of the time is spent in the solve, as expected. Is there a way to get around calling setProblem() every time I need to solve the linear system, or could I be doing something wrong?

Thank you,
John
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