[petsc-users] about pclu

[Matthew Knepley]

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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