[petsc-users] About the initial guess for KSP method.

[Xiaodong Liu]

Thanks. It is very useful.

Xiaodong Liu, PhD
X: Computational Physics Division
Los Alamos National Laboratory
P.O. Box 1663,
Los Alamos, NM 87544
505-709-0534


On Tue, Mar 17, 2020 at 8:17 AM Matthew Knepley <knepley at gmail.com> wrote:

> On Mon, Mar 16, 2020 at 4:32 PM Xiaodong Liu <xliu29 at ncsu.edu> wrote:
>
>> Hi, all,
>>
>> I am testing KSPSetInitialGuessNonzero using the case
>>
>>
>> https://www.mcs.anl.gov/petsc/petsc-current/src/ksp/ksp/examples/tutorials/ex50.c.html
>>
>> This case is special. WIth zero initial guess, 1 iteration can deliver
>> the exact solution. But when I tried true for KSPSetInitialGuessNonzero, it
>> shows the same convergence history as false.
>>
>> Does the code  change KSPSetInitialGuessNonzero to false automatically?
>>
>
> For that flag to make any difference, you have to pass in a nonzero vector
> to KSPSolve(). This example does not do that.
> Were you doing that?
>
>   Thanks,
>
>      Matt
>
>
>> Take care.
>>
>> Thanks,
>>
>> Xiaodong Liu, PhD
>> X: Computational Physics Division
>> Los Alamos National Laboratory
>> P.O. Box 1663,
>> Los Alamos, NM 87544
>> 505-709-0534
>>
>
>
> --
> 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
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>
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