Got it. I’m trying to build up my desired convergence test, based on the
default routine. I’m getting the following compiler error, which I don’t
entirely understand:
blowup_utils.c:180:9: error:
incomplete definition of type 'struct _p_SNES'
snes->ttol = fnorm_scaled*snes->rtol;
~~~~^
/opt/petsc/include/petscsnes.h:20:16: note: forward declaration of
'struct _p_SNES'
typedef struct _p_SNES* SNES;
Separately, is there a way to get the step vector?
-gideon
> On Jan 12, 2016, at 9:17 AM, Dave May <[email protected]> wrote:
>
>
>
> On 12 January 2016 at 15:06, <[email protected]
> <mailto:[email protected]>> wrote:
> Do I have to manually code in the divergence criteria too?
>
> Yes.
>
> By calling SNESSetConvergenceTest() you are replacing the default SNES
> convergence test function which will get called at each SNES iteration,
> therefore you are responsible for defining all reasons for convergence and
> divergence.
>
> To make life easy, you could copy everything in the funciton
> SNESConvergedDefault(),
>
> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/SNESConvergedDefault.html#SNESConvergedDefault
>
> <http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/SNESConvergedDefault.html#SNESConvergedDefault>
>
> and just replace the rule for
> SNES_CONVERGED_FNORM_RELATIVE
> with your custom scaled stopping condition.
>
>
>
>
>
>
> On Jan 12, 2016, at 8:37 AM, Dave May <[email protected]
> <mailto:[email protected]>> wrote:
>
>>
>>
>> On 12 January 2016 at 14:33, Gideon Simpson <[email protected]
>> <mailto:[email protected]>> wrote:
>> I’m just a bit confused by the documentation for
>> SNESConvergenceTestFunction. the arguments for the xnorm, gnorm, and f are
>> passed in, at the current iterate, correct?
>>
>> Yes, but nothing requires you to use them :D
>>
>> I interpreted this as though I had to build by convergence test based on
>> those values.
>>
>> This is a misinterpretation. You can ignore all of xnorm, gnorm and fnorm
>> and define any crazy stopping condition you like.
>>
>> xnorm, gnorm and fnorm are commonly required for many stopping conditions
>> and are computed by the snes methods. As such, are readily available and for
>> efficiency and convenience they are provided to the user (e.g. to avoid you
>> having to re-compute norms).
>>
>> Cheers,
>> Dave
>>
>>
>> -gideon
>>
>>> On Jan 12, 2016, at 8:24 AM, Dave May <[email protected]
>>> <mailto:[email protected]>> wrote:
>>>
>>>
>>>
>>> On 12 January 2016 at 14:14, Gideon Simpson <[email protected]
>>> <mailto:[email protected]>> wrote:
>>> That seems to to allow for me to cook up a convergence test in terms of the
>>> 2 norm.
>>>
>>> While you are only provided the 2 norm of F, you are also given access to
>>> the SNES object. Thus inside your user convergence test function, you can
>>> call SNESGetFunction() and SNESGetSolution(), then you can compute your
>>> convergence criteria and set the converged reason to what ever you want.
>>>
>>> See
>>>
>>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/SNESGetFunction.html
>>>
>>> <http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/SNESGetFunction.html>
>>>
>>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/SNESGetSolution.html
>>>
>>> <http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/SNESGetSolution.html>
>>>
>>> Cheers,
>>> Dave
>>>
>>>
>>>
>>>
>>> What I’m really looking for is the ability to change things to be something
>>> like the 2 norm of the vector with elements
>>>
>>> F_i/|x_i|
>>>
>>> where I am looking for a root of F(x). I can just build that scaling into
>>> the form function, but is there a way to do it without rewriting that piece
>>> of the code?
>>>
>>>
>>> -gideon
>>>
>>>> On Jan 12, 2016, at 12:14 AM, Barry Smith <[email protected]
>>>> <mailto:[email protected]>> wrote:
>>>>
>>>>
>>>> You can use SNESSetConvergenceTest() to use whatever test you want to
>>>> decide on convergence.
>>>>
>>>> Barry
>>>>
>>>>> On Jan 11, 2016, at 3:26 PM, Gideon Simpson <[email protected]
>>>>> <mailto:[email protected]>> wrote:
>>>>>
>>>>> I’m solving nonlinear problem for a complex valued function which is
>>>>> decomposed into real and imaginary parts, Q = u + i v. What I’m finding
>>>>> is that where |Q| is small, the numerical phase errors tend to be larger.
>>>>> I suspect this is because it’s using the 2-norm for convergence in the
>>>>> SNES, so, where the solution is already, the phase errors are seen as
>>>>> small too. Is there a way to use something more like an infinity norm
>>>>> with SNES, to get more point wise control?
>>>>>
>>>>> -gideon
>>>>>
>>>>
>>>
>>>
>>
>>
>
