[petsc-users] Solution Diverging

[Mark Adams]

On Fri, Apr 5, 2019 at 5:27 PM Maahi Talukder <maahi.buet at gmail.com> wrote:

> Hi,
> Thank you for your reply.
>
> Well, I have verified the solution on large problems, and I have converged
> the solution to machine accuracy using different solvers. So I guess the
> setup okay in that respect.
>

I am suspicious that it "worked" on large problems but failed on small. But
you never know.


>
> The BC I am using is of Dirichlet type.
>
>
>
> On Fri, Apr 5, 2019 at 5:21 PM Mark Adams <mfadams at lbl.gov> wrote:
>
>> So you have a 2D Poisson solver and it is working on large problems but
>> the linear solver is diverging on small problems.
>>
>> I would verify the the solution is good on the large problem.
>>
>> You might have a problem with boundary conditions. What BCs do you think
>> you are using?
>>
>> On Fri, Apr 5, 2019 at 4:33 PM Maahi Talukder via petsc-users <
>> petsc-users at mcs.anl.gov> wrote:
>>
>>> Dear All,
>>>
>>> I am solving a linear system arising from 9-point discretization of
>>> Poisson equation to generate grid. KSP solvers are giving nice converged
>>> result when I am dealing with a large matrix. But when I am trying to
>>> implement KSP solvers when the matrix is smaller and the values are smaller
>>> too, the solution is diverging.
>>> Any suggestions how to get around this problem?
>>>
>>>
>>> Regards,
>>> Maahi Talukder
>>>
>>>
>>>
>>>
>>>
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