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

[Franck Houssen]

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
>