[petsc-users] Checking if a vector is a localvector of a given DMDA

[Dave May]

On Tue, 25 Sep 2018 at 13:20, Matthew Knepley <knepley at gmail.com> wrote:

> On Tue, Sep 25, 2018 at 7:03 AM Dave May <dave.mayhem23 at gmail.com> wrote:
>
>> On Tue, 25 Sep 2018 at 11:49, Phil Tooley <phil.tooley at sheffield.ac.uk>
>> wrote:
>>
>>> Hi all,
>>>
>>> Given a vector I know I can get an associated DM (if there is one) by
>>> calling VecGetDM, but I need to also be able to check that
>>>
>>> a) the vector is the localvector of that DM rather than the global
>>>
>>
>> Given the vector, you can check the communicator size via
>> PetscObjectGetComm()
>>
>>
>> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PetscObjectGetComm.html
>> and then MPI_Comm_size()
>> If the comm size 1, it is local vector.
>>
>
> In serial, both vectors have comm size 1.
>

Right - and the local and global sizes are the same.

 My point was to check the comm size first. If it's 1 then you have a
candidate for a local vector. Then you'd check the vec global size matches
the dmda local size. If the commsize is anything other than 1 then it
cannot be a local vector


>    Matt
>
>
>> You can check the size matches your local DMDA space by using
>> DMDAGetGhostCorners()
>>
>>
>> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/DMDA/DMDAGetGhostCorners.html
>>
>> and return the quantities m, n, and p.
>>
>> You also need to use  DMDAGetInfo()
>>
>>
>> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/DMDA/DMDAGetInfo.html
>>
>> The important quantity you want returned is "dof"
>>
>> If m x n x p x dof matches the number returned by VecGetSize() (assuming
>> you know the vector is sequential) then you know the local space will fit
>> within your vector.
>>
>>
>>
>>>
>>> b) the DM is a DMDA rather than some other subclass
>>>
>>
>> See Matt's answer
>>
>>
>>>
>>> I can't immediately see routines that do what I need, but I am likely
>>> missing something obvious. Is there a way to achieve the above?
>>>
>>> Thanks
>>>
>>> Phil
>>>
>>> --
>>> Phil Tooley
>>> Research Software Engineering
>>> University of Sheffield
>>>
>>>
>
> --
> 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
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20180925/d113ae9d/attachment.html>