[petsc-dev] MatISGetLocalMat: need to MatDestroy the returned local matrice ?

[Stefano Zampini]

Franck,

if you get the local mat, you are free to do whatever you want with it. One possible case is that you create the MATIS object (i.e., basically a l2g map of dofs + local mat creation) and then do

MatISGetLocalMat(matis,&A);
MatXAIJSetPreallocation(A,…..)
MatSetValues(A,…)

What do you need it for?

Stefano

> On May 19, 2017, at 4:57 PM, Franck Houssen <franck.houssen at inria.fr> wrote:
> 
> Thanks.
> 
> My understanding (?) is that modifying the local mat (with MatMult for instance) changes also the global mat (as the local mat is a part of the global one). Jed, I let you decide if this behavior (which is logical but not always the desired one) is worth to be emphasized in the doc...
> 
> Franck
> 
> ----- Mail original -----
>> De: "Jed Brown" <jed at jedbrown.org>
>> À: "Franck Houssen" <franck.houssen at inria.fr>, petsc-dev at mcs.anl.gov
>> Envoyé: Vendredi 19 Mai 2017 16:20:14
>> Objet: Re: [petsc-dev] MatISGetLocalMat: need to MatDestroy the returned local	matrice ?
>> 
>> Thanks.  I just pushed this.
>> 
>> commit 96a6f12955a790d77f6eb7eb6b1dcf9dd5e1cf30
>> Author: Jed Brown <jed at jedbrown.org>
>> Date:   Fri May 19 08:17:45 2017 -0600
>> 
>>    MatISGetLocalMat: add note on reference counting
>> 
>>    Reported-by: Franck Houssen <franck.houssen at inria.fr>
>> 
>> diff --git a/src/mat/impls/is/matis.c b/src/mat/impls/is/matis.c
>> index dc4a894aae..287c0aa554 100644
>> --- a/src/mat/impls/is/matis.c
>> +++ b/src/mat/impls/is/matis.c
>> @@ -837,6 +837,9 @@ PetscErrorCode MatISGetLocalMat_IS(Mat mat,Mat *local)
>>   matrix and want to provide it to the inner matrix object to improve the
>>   performance
>>   of the MatSetValues() operation.
>> 
>> +  This function does not increase the reference count for the local Mat.  Do
>> not destroy it and do not attempt to use
>> +  your reference after destroying the parent mat.
>> +
>> .seealso: MATIS
>> @*/
>> PetscErrorCode MatISGetLocalMat(Mat mat,Mat *local)
>> 
>> Franck Houssen <franck.houssen at inria.fr> writes:
>> 
>>> Hello,
>>> 
>>> Do I need to MatDestroy the local matrix returned by MatISGetLocalMat ?
>>> (the global matrix has been created with MatCreateIS)
>>> 
>>> Tried to look in the source tree... But I'am not sure to get the answer: in
>>> petsc-3.7.6/src/mat/impls/is/matis.c, MatISGetLocalMat seems to call
>>> MatISGetLocalMat_C, but, I can't find MatISGetLocalMat_C in the source
>>> tree !?...
>>> 
>>> Franck
>>