[petsc-users] [Ext] change matrix

[Barry Smith]

> On Aug 31, 2020, at 2:08 PM, Kun Jiao <KJiao at slb.com> wrote:
> 
> If I am correct, to do this, it will double the peak memory usage.

  Yes

>  
> Is there any way no to double the peak memory usage?

  The only way would be to destroy the old matrix, allocate a new one and recompute the entries. 

  Barry

  Depending on the application etc the extra memory for storing two copies of the matrix may not be a fundamental problem.
>  
>  
>  
> Schlumberger-Private
> From: Barry Smith <bsmith at petsc.dev <mailto:bsmith at petsc.dev>> 
> Sent: Monday, August 31, 2020 1:56 PM
> To: Kun Jiao <KJiao at slb.com <mailto:KJiao at slb.com>>
> Cc: petsc-users <petsc-users at mcs.anl.gov <mailto:petsc-users at mcs.anl.gov>>
> Subject: [Ext] Re: [petsc-users] change matrix
>  
>  
>   Kun,
>  
>    This is not possible, PETSc matrices have a static size (resizing in parallel is tricky so we don't support it). 
>  
>    If it is more efficient to reuse the matrix entries than recompute them you can create a larger matrix and then loop over the old matrix calling MatGetRow() and then call MatSetValues() to copy that row into the new matrix.
>  
>   Barry
>  
>  
> 
> On Aug 31, 2020, at 1:51 PM, Kun Jiao via petsc-users <petsc-users at mcs.anl.gov <mailto:petsc-users at mcs.anl.gov>> wrote:
>  
> Hi Petsc Experts,
>  
> Trying to do something like appending some rows (~100 rows) to an already created matrix, but could not find any document about it.
>  
> Could anyone provide some information about it?
>  
> Regards,
> Kun
>  
> Schlumberger-Private

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