[petsc-users] Accessing Vector's ghost values

[Mohammad Mirzadeh]

just index x with the local numberings. if you have 'n' local nodes and 'g'
ghost nodes in x, ghost nodes indecies run from 'n' to 'n+g-1'
On Feb 23, 2012 1:16 PM, "Bojan Niceno" <bojan.niceno at psi.ch> wrote:

>  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> 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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