[petsc-dev] snes_type test

[Mark Adams]

I see, I had a tiny time step that make the Jacobian big and the errors
small.

On Thu, Aug 17, 2017 at 12:30 AM, Mark Adams <mfadams at lbl.gov> wrote:

>
>
> On Thu, Aug 17, 2017 at 12:22 AM, Matthew Knepley <knepley at gmail.com>
> wrote:
>
>> On Wed, Aug 16, 2017 at 10:14 AM, Mark Adams <mfadams at lbl.gov> wrote:
>>
>>> I just want to check the interpretation of snes_type test. Is this
>>> pretty conclusively good?
>>>
>>
>> It looks right, but the entires in the Jacobian are crazy. You should
>> non-dimensionalize first.
>>
>
> This is non-dimensionalize and it is 2D FE 2nd order equation so
> everything should be O(1), that is, there is no 1/h like term. And the
> domain is (1) and the grid is small so h is O(1) anyway.
>
>
>>
>>   Matt
>>
>>
>>> Testing hand-coded Jacobian, if the ratio is
>>> O(1.e-8), the hand-coded Jacobian is probably correct.
>>> Run with -snes_test_display to show difference
>>> of hand-coded and finite difference Jacobian.
>>> Norm of matrix ratio 1.38299e-16, difference 1.11738 (user-defined state)
>>> Norm of matrix ratio 9.50529e-09, difference 7.67972e+07 (constant state
>>> -1.0)
>>> Norm of matrix ratio 1.07438e-08, difference 8.68036e+07 (constant state
>>> 1.0)
>>>
>>>
>>
>>
>> --
>> 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
>>
>> http://www.caam.rice.edu/~mk51/
>>
>
>
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