[petsc-users] Get Stuck in SNES

behzad baghapour behzad.baghapour at gmail.com
Thu Nov 24 05:37:37 CST 2011


I meant that to do just one or two step in line search correction and let
the solution goes on even if the error reduction may not reach the desired
tolerance. It may help to reduce the computational cost especially in first
iteration or in almost ill-conditioned situation where the Newton iteration
may not holds the stability or does not lead to correct solution and a
change in preconditioning is needed to overcome the situation.



On Thu, Nov 24, 2011 at 2:39 PM, Matthew Knepley <knepley at gmail.com> wrote:

> On Thu, Nov 24, 2011 at 5:00 AM, behzad baghapour <
> behzad.baghapour at gmail.com> wrote:
>
>>
>>
>> On Wed, Nov 23, 2011 at 4:33 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
>>
>>> On Wed, Nov 23, 2011 at 01:06, behzad baghapour <
>>> behzad.baghapour at gmail.com> wrote:
>>>
>>>>     for( c=0; c<ne; c++ ) for( p=0; p<tot; p++ )
>>>>     FC->e[c].Q[p] = xx[c*(noe*num)+p];
>>>>
>>>
>>> You haven't told me about "noe" or "num". Do you mean for this to read
>>> xx[c*tot+p]?
>>>
>>
>> noe is the number of equations (equal to number of flow states) and num
>> is the number of shape functions in element (according to the order of
>> accuracy)
>>
>>>
>>>
>>>>
>>>>     ierr = VecRestoreArray( x, &xx ); CHKERRQ( ierr );
>>>>
>>>>     interiorFlux( FC->flw, FC->e );
>>>>     faceFlux    ( FC->flw, FC->f, FC->e );
>>>>
>>>
>>> The first of these should set FC->e (if you are adding into it, then you
>>> need to zero it first) and the second should add into it.
>>>
>>
>> I found that my mistake is that I forgot to set upwind effect in my
>> defined field context. The problem was not stable, it is not related to
>> SNES setup.
>>
>> However, I can't find out the difference between "basic" and
>> "basicnonorms" in line search method.
>>
>
> Basic takes the full Newton step, but checks for decrease. nonorms just
> takes it and moves on.
>
>
>> In addition, Is it possible to set the number of line-search corrections
>> or is just decided by the solver?
>>
>
> You can set a custom line search. I am not sure what you mean by this
> "number of line search correctons"
>
>    Matt
>
>
>> Thanks a lot,
>> BehZad
>>
>>
>>
>
>
> --
> 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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