[petsc-users] VecSet and VecAssemblyBegin

[Barry Smith]

   Technically you should not be calling VecSet() with any outstanding arrays but it will probably be fine.

    Even though GetArray() does not copy the array values; both GetArray/RestoreArray and Set track the current "state" of the vector and that count might get confused if they are used improperly.



> On Apr 25, 2025, at 4:42 PM, Derek Teaney <derek.teaney at stonybrook.edu> wrote:
> 
> Thanks,   I am working on providing a standalone code. A related question is -  if I did have a view of a local vector provided by:
> 
> data_node ***dn_array;
> DMDAVecGetArray(domain, dn_local, &dn_array);
> 
> Can I assume through multiple calls to VecSet that the view  dn_array is valid, or should this be restored, between calls.
> 
> Thanks, 
> 
> Derek
> 
> On Fri, Apr 25, 2025 at 1:26 PM Barry Smith <bsmith at petsc.dev <mailto:bsmith at petsc.dev>> wrote:
>>   
>>    You absolutely should not need to do an assembly after a VecSet. Please post a full reproducer that demonstrates the problem.
>> 
>>   Barry
>> 
>> 
>>> On Apr 25, 2025, at 1:23 PM, Derek Teaney via petsc-users <petsc-users at mcs.anl.gov <mailto:petsc-users at mcs.anl.gov>> wrote:
>>> 
>>> Hi, 
>>> 
>>> I was under the (mistaken) impression that one does not need to due a VecAssemblyBegin etc following a VecSet, e.g. 
>>> 
>>>       VecSet(dn_local, 0.);
>>>       VecAssemblyBegin(dn_local) ;
>>>       VecAssemblyEnd(dn_local) ;
>>> 
>>> Seems to give different results without the Assembly.  
>>> 
>>> Thanks for clarifying, 
>>> 
>>> Derek
>>> 
>>> --
>>> ------------------------------------------------------------------------
>>> Derek Teaney
>>> Professor and Graduate Program Director
>>> Dept. of Physics & Astronomy
>>> Stony Brook University
>>> Stony Brook, NY 11794-3800
>>> Tel: (631) 632-4489
>>> Fax: (631) 632-9718
>>> e-mail: Derek.Teaney at stonybrook.edu <mailto:Derek.Teaney at stonybrook.edu>
>>> ------------------------------------------------------------------------
>>> 
>> 
> 
> 
> 
> --
> ------------------------------------------------------------------------
> Derek Teaney
> Professor and Graduate Program Director
> Dept. of Physics & Astronomy
> Stony Brook University
> Stony Brook, NY 11794-3800
> Tel: (631) 632-4489
> Fax: (631) 632-9718
> e-mail: Derek.Teaney at stonybrook.edu <mailto:Derek.Teaney at stonybrook.edu>
> ------------------------------------------------------------------------
> 

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