[petsc-users] question on MatSubMatrixUpdate

[Matthew Knepley]

On Mon, May 6, 2013 at 4:00 PM, Shaohao Chen <shchen at www.phys.lsu.edu>wrote:

> Dear managers and users,
>
> I got a problem when using PETSc to make parallel codes. Could you please
> help me out?
>
> Basically, I need to do is to update the values of some blocks of a large
> matrix (not the whole matrix),
> and I need to do it many times in a big loop. These blocks could be
> assembled to the same or
> different processors. If using "MatSetValues", it would spend much time
> for the data transfer between
>

Are you guessing, or have you measured this?


> different processors. I expect "MatSubMatrixUpdate" could do the job
> better. Am I correct? But I can
>

Almost certainly not. It cannot do less communication than MatSetValues(),
its just easier sometimes.

   Matt


> not find an example of using "MatSubMatrixUpdate" on the website. It is
> said that the
> "MatSubMatrixUpdate" is only in a "developer" level and the users should
> use some other functions to
> replace it. What other functions should I use?
>
> Thank you for your attention!
>
> --
> Shaohao Chen
> Department of Physics & Astronomy,
> Louisiana State University,
> Baton Rouge, LA
>



-- 
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
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