[petsc-users] about pclu

[Ryan Yan]

I see. Thanks, Matt.

Yan

On Tue, Apr 5, 2011 at 11:27 PM, Matthew Knepley <knepley at gmail.com> wrote:

> On Tue, Apr 5, 2011 at 10:20 PM, Ryan Yan <vyan2000 at gmail.com> wrote:
>
>> One more ask, :-)
>>
>> Which one is more efficient, richardson, preonly or no difference, if I am
>> going to use direct solver for many times steps.
>>
>
> There should be no difference since direct solves take so long.
>
>   Matt
>
>
>> Thanks,
>>
>> Yan
>>
>> On Tue, Apr 5, 2011 at 11:06 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>>
>>>
>>> On Apr 5, 2011, at 9:52 PM, Ryan Yan wrote:
>>>
>>> > Hi,
>>> > I am wondering is there a way of checking the residual of a direct
>>> solver. It should
>>> > be one shot and very small.  I tried -ksp_monitor_true_residual, but no
>>> thing shows up. I guess a piece of code
>>> > $Ax-b$ will do the trick?
>>>
>>>    The reason that the monitor doesn't display anything is not the direct
>>> solver but because you are using LU with KSPType of KSPPREONLY  if you run
>>> with -ksp_type richardson or -ksp_type gmres then -ksp_monitor_true_residual
>>> will print the residual as you want.
>>>
>>>   Barry
>>>
>>> >
>>> > Thanks,
>>> >
>>> > Yan
>>>
>>>
>>
>
>
> --
> 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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