[petsc-users] dmmg_grid_sequence

[Matthew Knepley]

On Mon, Apr 2, 2012 at 10:11 AM, Xuefeng Li <li at loyno.edu> wrote:

> Hi, all.
>
> I am using multigrid with DMMG (5 levels) in my petsc program.
> Turning on the dmmg_grid_sequence option seems
> to slow down the program dramatically. For instance,
> the program converges in 3 iterations in 6.270e+01 sec
> when dmmg_grid_sequence is OFF; it also converges
> in 3 iterations but in 1.699e+04 sec when dmmg_grid_sequence
> is ON.
>
> Is this typical of petsc (I'm using petsc-3.1-p8)?
> Are there ways to improve the performance when
> dmmg_grid_sequence is ON?
>

Its impossible to know what is happening from this description. There is no
"generic" performance of grid sequencing. The best thing I can say to this
is,
it looks like the interpolated solution to your coarse problem is not a
great
solution to your fine problem. However, you could be oversolving the coarse
problems, blowing up the work, or interpolating badly for your problem.

    Matt


> Regards,
>
> --Xuefeng Li, (504)865-3340(phone)
>  Like floating clouds, the heart rests easy
>  Like flowing water, the spirit stays free
>       http://www.loyno.edu/~li/home
>  New Orleans, Louisiana (504)865-2051(fax)
>
>


-- 
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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