[petsc-users] slower in petsc

[Matthew Knepley]

On Thu, Aug 25, 2011 at 4:58 PM, Likun Tan <likunt at andrew.cmu.edu> wrote:

> Hello,
>
> I am computing Ax=b, while using petsc (currently uniprocessor) the
> computation is much slower.
>
> I realize generation of the matrix is very time-consuming, the elements
> are integrals of functions with complicated form, i.e.\\\int(f(r(x,y,z),
> s(x,y,z), t(x,y,z), phi(x,y,z,node)dxdydz, where the shape function has
> different forms on each node. In my C code, i calculated r, s, t and phi
> on the integration points first and saved the data in 3D array. In petsc,
> i use the same strategy by applying DA to set values to r, s, t and phi on
> each integration points.
>
> Since i need to solve Ax=b for million times, A is changing every time and
> i use DAVecGetArray repeatly, is that the reason for low efficiency and
> any suggestions for performance enhancement?
>
> btw, calculation of r,s,t..is the only part i use parallel computing,
> since I think the assemble of A and b is fast once the entries have been
> computed.
>

There is no way to know what you are doing. As we say online and in the
manual,
configure with --with-debugging=0, look at the performance guidance chapter,
and send the output of -log_summary to petsc-maint at mcs.anl.gov.

    Matt


> Thanks,
> Likun
>
>
>
>


-- 
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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