[petsc-users] DMCreateMatrix with some dense row

[Barry Smith]

> On Oct 24, 2015, at 1:43 AM, Sang pham van <pvsang002 at gmail.com> wrote:
> 
> Thank you, Dave,
> 
> Can I just call My_DMCreateMatrix_DA_3d_MPIAIJ(DM da, Mat J, void* my_context) when I need to create my matrix, and forget about DMDASetGetMatrix()?

  You can do that if that is all you need. In some contexts when something else in PETSc needs to create a specific matrix (like with geometric multigrid) then that code calls DMCreateMatrix() which would then use your creation routine. 

   So, in summary you can start by just calling your own routine and convert it to use DMSetGetMatrix() later if you need to.

  Barry

> 
> Thank you.
> 
> Pham
> 
> On Sat, Oct 24, 2015 at 1:33 PM, Dave May <dave.mayhem23 at gmail.com> wrote:
> If you need to access a user defined context from within your CreateMatrix function, you can attach it to the DM via PetscObjectCompose
> 
> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PetscObjectCompose.html
> 
> If your context is not a petsc object, you can use PetscContainerCreate(), 
> 
> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PetscContainerCreate.html#PetscContainerCreate
> 
> You would then set your user context pointer inside the container and then use PetscObjectCompose() to attach the container to the DM
> 
> Thanks,
>   Dave
> 
> 
> On 24 October 2015 at 06:04, Sang pham van <pvsang002 at gmail.com> wrote:
> Hi Barry,
> 
> The routine DMCreateMatrix_DA_3d_MPIAIJ has 2 input arguments (DM da, Mat J), the function pointer in DMDASetGetMatrix() only accept function with that two arguments. 
> As you suggested, I am writing a routine (based on DMCreateMatrix_DA_3d_MPIAIJ()) to preallocate the matrix in the way I wish, to do that I think It needs to have one more input argument: My_DMCreateMatrix_DA_3d_MPIAIJ(DM da, Mat J, void* my_context). But DMDASetGetMatrix() will not accept pointer of this function. Please give a suggestion to overcome this.
> 
> Thank you.
> 
> Pham
> 
> 
> On Fri, Sep 4, 2015 at 1:24 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> 
>     Look at DMCreateMatrix_DA_2d_MPIAIJ  (or the 3d version if working in 3d)   You need to copy this routine and add whatever additional preallocation information you need.   Then call DMDASetGetMatrix()  so that the DM will use your routine to create the matrix for you.
> 
>    Barry
> 
> 
> 
> 
> > On Sep 3, 2015, at 11:28 AM, Sang pham van <pvsang002 at gmail.com> wrote:
> >
> > Hi,
> >
> > I am using DMCreateMatrix to create matrix from a existed DM object and defined stencil.
> > In my code, boundary nodes need to involve many inner nodes, thus matrix rows corresponding to boundary nodes are almost dense. How can I  tell petsc that those rows need to be preallocated with more entries? I don't want to use MatMPIAIJSetPreallocation() since advantages of DM might be lost.
> >
> > Many thanks.
> >
> > Sam.
> >
> >
> 
> 
> 
>