[petsc-users] Matrix Factorization fill

[Matthew Knepley]

On Tue, Sep 20, 2011 at 7:02 PM, Rongliang Chen <rongliang.chan at gmail.com>wrote:

> Hi,
>
> I have a question about the Sparse Matrix Factorization fill.
> Following the manual, I use the option "-info" and get the following
> result:
>
> [0] MatLUFactorSymbolic_SeqAIJ(): Reallocs 0 Fill ratio:given 5 needed
> 5.0746e-05
> [0] MatLUFactorSymbolic_SeqAIJ(): Run with -pc_factor_fill 5.0746e-05 or
> use
> [0] MatLUFactorSymbolic_SeqAIJ(): PCFactorSetFill(pc,5.0746e-05);
>
> What's the numbers mean in "Reallocs 0 Fill ratio:given 5 needed
> 5.0746e-05"?
> Does the " Run with -pc_factor_fill 5.0746e-05 or use" mean that I should
> run my code with option " -pc_factor_fill 5.0746e-05"?
>

"Reallocs 0": no additional malloc()s were needed

"Fill rato: give 5 needed 5.0746e-05" We guessed that the factor would need
5 times the matrix memory. It actually needed a lot less.

If you run -pc_factor_fill 5.0746e-05, you will get the same performance and
use a lot less memory.

    Matt


> But when I run my code with option "-snes_view", I get "factor fill ratio
> given 5, needed 3.28701".
> So what should I give to the option "-pc_factor_fill", 3.28701 or
> 5.0746e-05? Thanks.
>
> Best,
> Rongliang
>



-- 
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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