[petsc-users] Accessing Vector's ghost values

[Bojan Niceno]

Dear Jed,

thanks.

Now I have the following:

- Array unk, which should hold values inside the partition and in ghost 
cells.  It is big enough to hold both
- Vec x, created by command VecCreateGhost, with proper padding for 
ghost cells
- Successful call to linear solver in parallel.

But I need to copy ghost values from x to my array unk.

How can I do it?


     Kind regards,


     Bojan

On 2/23/2012 10:10 PM, Jed Brown wrote:
> On Thu, Feb 23, 2012 at 15:05, Bojan Niceno <bojan.niceno at psi.ch 
> <mailto:bojan.niceno at psi.ch>> wrote:
>
>     No, I use global.
>
>
> The local form is just a local vector. It doesn't even know that a 
> global problem exists. You can't index into it using global indices. 
> (In general, there is no efficient way to look up information in the 
> local vector (includes ghost points) using global indices.)
>
>
>       for(Int i=0; i<n; i++) {
>         Int gi = mesh.nodes[i].global_number;
>         VecGetValues(x, 1, &gi, &unk[i]);
>       }
>
>     "n" is defined as the number of cells inside, i.e. without
>     buffers.  "unk" is my external array.  If I try to access buffer
>     values, I use:
>
>       for(Int i=0; i<N; i++) {
>         Int gi = mesh.nodes[i].global_number;
>         VecGetValues(x, 1, &gi, &unk[i]);
>       }
>
>     But then I end up with tons of warnings, presumably because I am
>     going beyond "n".  Vector x was created with VecCreateGhost.
>
>


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