[petsc-dev] Some questions about adding default global to local, etc., functions for DMShell

[Barry Smith]

On Mar 6, 2013, at 2:18 PM, Matthew Knepley <knepley at gmail.com> wrote:

> On Wed, Mar 6, 2013 at 2:54 PM, Richard Tran Mills <rtm at eecs.utk.edu> wrote:
> Hi Folks,
> 
> I am adding some pointers to scatter contexts within the internal "data" struct for DMShell, e.g. the 'gtol' and 'ltog' members in
> 
> typedef struct  {
>   Vec Xglobal;
>   Vec Xlocal;
>   Mat A;
>   VecScatter *gtol;
>   VecScatter *ltog;
> } DM_Shell;
> 
> First question: When in DMCreate_Shell we do
> 
> ierr     = PetscNewLog(dm,DM_Shell,&shell);CHKERRQ(ierr);
> 
> will this guarantee that gtol and ltog are set to NULL, or do I need to explicitly set these somewhere?  I see that the allocated memory is zeroed but I'm not sure how NULL might actually be represented in memory.
> 
> Yes, they will be NULL.
>  
> I have also added some new functions like DMShellDefaultGlobalToLocalBegin()/End(), and in DMCreate_Shell I do 
> 
>   dm->ops->globaltolocalbegin = DMShellDefaultGlobalToLocalBegin;
>   dm->ops->globaltolocalend   = DMShellDefaultGlobalToLocalEnd;
> 
   Bad names. Since they are not user functions they should have an underscore in them and specification of implementation after the underscore. Perhaps  DMGlobalToLocalBegin_Shell_Default?

    Check out the PETSc developers manual style guide (which is now chapter one so people actually read it :-)) Section 1.1 and 1.2 http://www.mcs.anl.gov/petsc/developers/developers.pdf


   Barry



> The user can set different routines via DMShellSetGlobalToLocalBegin()/End(), but if the user only sets the gtol and ltog scatter contexts, then the default routines will perform the appropriate scatter operations.
> 
> Second question: What is the proper "PETSc way" to throw an error if gtol is NULL and tell the user that DMShellDefaultGlobalToLocalBegin() cannot be used without first setting the scatter context via DMShellSetGlobalToLocalVecScatter()?
> 
> SETERRQ(comm, PETSC_ERR_ARG_WRONGSTATE, "DMShellDefaultGlobalToLocalBegin() cannot be used without first setting the scatter context via DMShellSetGlobalToLocalVecScatter()");
> 
>    Matt
>  
> Thanks,
> Richard
> 
> 
> 
> -- 
> Richard Tran Mills, Ph.D.
> Computational Earth Scientist      | Joint Assistant Professor
> Hydrogeochemical Dynamics Team     | EECS and Earth & Planetary Sciences
> Oak Ridge National Laboratory      | University of Tennessee, Knoxville
> E-mail: 
> rmills at ornl.gov  V: 865-241-3198 http://climate.ornl.gov/~rmills
> 
> 
> 
> -- 
> 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