[petsc-users] using '-snes_type test' to test my coded Jacobian

[Zou (Non-US), Ling]

==================================================
Framework Information:
SVN Revision:            13656
PETSc Version:           3.1.0
Current Time:            Wed Sep 19 14:17:01 2012
Executable Timestamp:    Wed Sep 19 14:14:46 2012
==================================================

I believe my version is 3.1.0.

Ling



On Wed, Sep 19, 2012 at 2:31 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> Are you using an older version of PETSc?
>
>
> On Wed, Sep 19, 2012 at 2:56 PM, Zou (Non-US), Ling <ling.zou at inl.gov>wrote:
>
>> No Jacobian output showed when I did this,
>>
>> ./my-project-opt -i input.i -snes_compare_explicit
>>
>> Any suggestion?
>>
>> Ling
>>
>>
>>
>> On Wed, Sep 19, 2012 at 1:12 PM, Zou (Non-US), Ling <ling.zou at inl.gov>wrote:
>>
>>>
>>>
>>> On Wed, Sep 19, 2012 at 1:03 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
>>>
>>>> On Wed, Sep 19, 2012 at 1:54 PM, Zou (Non-US), Ling <ling.zou at inl.gov>wrote:
>>>>
>>>>> Dear Matt,
>>>>>
>>>>> Thanks again for helping me on the '-snes_type test' issue. This is a
>>>>> great tool which helped us make really good progress recently.
>>>>>
>>>>> I have couple of more questions about the '-snes_type test'. From my
>>>>> understanding, this finite difference method is based on a tiny
>>>>> perturbation from a base solution vector. This base solution vector, from
>>>>> my observation, seems to be [1, 1, 1, ....].  However, this solution vector
>>>>> sometimes is very far from real physics, which causes issue, for example a
>>>>> dependent pressure variable get negative value.
>>>>>
>>>>> I wonder,
>>>>> 1), if this [1, 1, 1, ...] base solution vector is always used during
>>>>> the real simulation, for example when using the finite difference
>>>>> preconditioner. Or this base solution vector will change as solution gets
>>>>> updated?
>>>>>
>>>>
>>>> -snes_type test tries three different states: your user-defined state,
>>>> then constant -1.0, then constant +1.0. It does not solve the system so you
>>>> can't continue stepping, but you can just look at the result from the first
>>>> test.
>>>>
>>>
>>> Ahhh....... I see, that's why I always see three comparisons there. The
>>> first one should help me better when dealing with real simulation case.
>>>
>>>>
>>>>
>>>>> 2), is it possible to choose a different base solution, for example,
>>>>> [1000, 1000, 1000, 10, 10, 10, 1.e9, 1.e9, 1.e9] as the base solution
>>>>> vector when using the '-snes_type test'  option to test my hand-coded
>>>>> Jacobian.
>>>>>
>>>>
>>>> You can also use -snes_compare_explicit which shows the matrix (only
>>>> linearized around your actual state) and actually solves the system. There
>>>> is also -snes_compare_explicit_draw. If you know that you preallocated
>>>> correctly, -snes_compare_coloring is better. Details here.
>>>>
>>>>
>>>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/SNESComputeJacobian.html
>>>>
>>>
>>> This is something new to me. I'd take a look at the link. Thanks a lot,
>>> Jed.
>>>
>>> Best,
>>>
>>> Ling
>>>
>>>
>>
>
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