[petsc-users] How_to_get_other_processor's_portion_of_a_vector

[Youjun Hu]

It turns out I asked a question that is on the FAQ page:
How do I access the values of a parallel PETSc vector on a different
process than owns them?

   - On each process create a local vector large enough to hold all the
   values it wishes to access
   - Create a VecScatter that scatters from the parallel vector into the
   local vectors
   - Use VecGetArray() to access the values in the local vector



On Sun, Jul 29, 2018 at 11:42 PM, Youjun Hu <youjunhu at gmail.com> wrote:

> After doing some research, I am convinced that VecScatter is the proper
> subroutine to use in getting off-process values of a vector.
> Thank Jed.
> Youjun
>
> On Sun, Jul 29, 2018 at 10:36 PM, Jed Brown <jed at jedbrown.org> wrote:
>
>> See VecScatter.
>>
>> Youjun Hu <youjunhu at gmail.com> writes:
>>
>> > Hi all,
>> >
>> > The man-page for VecGetValues subroutine states that:
>> > "VecGetValues gets values from certain locations of a vector. Currently
>> can
>> > only get values on the same processor ".
>> >
>> > I am wondering whether there is a subroutine that can be used to get
>> values
>> > from any portion of a vector, rather than limited to the current
>> > processor's portion of the vector?
>> >
>> > It seems natural to expect that PETSc provides this kind of capability,
>> > which is already there for some subroutines, e.g., VecSetValues.
>> >
>> > When using VecSetValues to set the values of a vector, one processor can
>> > set other processors' portion of the vector. The communication is
>> handled
>> > by PETSc when VecAssembly is called.
>> >
>> > Am I missing something obvious?
>> > Cheers,
>> > Youjun
>>
>
>
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