[petsc-users] PETSCFE_CLASSID/PETSCVF_CLASSID

[Nicolas Barral]

Thanks Matt and Jacob,

There's still something not working yet, but I'm trying to build a MFE 
before asking.

Matt, what you say is consistent with plex/tutorials/ex8.c, but not with 
DMAdaptorAdapt_Sequence_Private. Does that mean that the latter is broken ?

Thanks

-- 
Nicolas

On 11/12/2020 18:39, Matthew Knepley wrote:
> On Fri, Dec 11, 2020 at 12:02 PM Nicolas Barral 
> <nicolas.barral at math.u-bordeaux.fr 
> <mailto:nicolas.barral at math.u-bordeaux.fr>> wrote:
> 
>     Hi all (and probably more specifically Matt ?)
> 
>     I am trying to understand how the class IDs of a DM field are set, and
>     can't find it in the documentation.
> 
>     A little background, I am mimicking
>     SNES/utils/dmadapt.c/DMAdaptorAdapt_Sequence_Private for a specific
>     case
>     (I'm trying to build the same kind of metric from a single sensor
>     field,
>     without all the SNES layer).
> 
>     I need to compute the gradient of the sensor field, using
>     DMPlexComputeGradientClementInterpolant, for which I create a DM, to
>     which I associate a PetscFE, a DS, like in existing code:
> 
>     PetscFE  feGrad
>     PetscDS  probGrad
> 
>     ierr = PetscFECreateDefault(PetscObjectComm((PetscObject) dmGrad), dim,
>     coordDim, PETSC_TRUE, NULL, -1, &feGrad);CHKERRQ(ierr);
>     ierr = PetscDSSetDiscretization(probGrad, f, (PetscObject)
>     feGrad);CHKERRQ(ierr);
> 
> 
> Jacobi is correct, so let me give the history. Originally, you were to 
> call PetscDSSetDiscretization() as you have done.
> However, now it is possible to have different discretization within the 
> same domain, So now we want you to call
> DMAddField(dm, feGrad), and then DMCreateDS(), which will 
> call PetscDSSetDiscretization() for you. I changed the
> examples, but I did not have another place to document this.
> 
>    Thanks,
> 
>       Matt
> 
>     ierr = PetscFEDestroy(&feGrad);CHKERRQ(ierr);
> 
>     Yet, when I call DMPlexComputeGradientClementInterpolant, I get the
>     following error:
>     [0]PETSC ERROR: Unknown discretization type for field 0
> 
>     I don't fully understand what all these objects are (FE, DS and Field),
>     and how they are related, where would that be documented ?
>     And what else do I need to do to make my example work ?
> 
>     Thanks
> 
>     -- 
>     Nicolas
> 
> 
> 
> -- 
> 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/>