[petsc-users] Matrix reuse with changing structure

[Barry Smith]

> On Mar 15, 2016, at 12:56 PM, Smith, Kevin R. <Kevin.R.Smith at jhuapl.edu> wrote:
> 
> 
> Barry - Yeah, I suspected it was doing this. In my original implementation I would get allocation errors. 

   You need to call a MatSetOption() to tell the matrix that it is allowed to allocate new nonzeros.


> 
> Matt - Thanks, I will try this solution out. 
> 
> Thanks for your help,
> 
>  Kevin
> 
> -----Original Message-----
> From: Barry Smith [mailto:bsmith at mcs.anl.gov] 
> Sent: Tuesday, March 15, 2016 1:48 PM
> To: Matthew Knepley
> Cc: Smith, Kevin R.; petsc-users at mcs.anl.gov
> Subject: Re: [petsc-users] Matrix reuse with changing structure
> 
> 
>> On Mar 15, 2016, at 12:28 PM, Matthew Knepley <knepley at gmail.com> wrote:
>> 
>> On Tue, Mar 15, 2016 at 12:24 PM, Smith, Kevin R. <Kevin.R.Smith at jhuapl.edu> wrote:
>> Hello,
>> 
>> 
>> 
>> Is it possible to reuse a sparse matrix and not reuse its non-zero structure?   I have a matrix whose sparse structure changes each time. I’m hoping to avoid destroying and allocating new matrices each time the structure changes.
> 
>   Sure you can just add new nonzero locations at a later time. But it won't take out any current entries even if they are zero. So effectively the nonzero structure grows over time.
> 
>   Barry
> 
>> 
>> 
>> Hmm, I can't find a toplevel API that does this (it would be something like MatReset()). You can get this effect using
>> 
>>  MatSetType(A, MATSHELL)
>>  MatSetType(A, <type you had before>)
>> 
>> A little messy but it will work.
>> 
>>  Thanks,
>> 
>>     Matt
>> 
>> 
>> 
>> Thanks,
>> 
>>  Kevin
>> 
>> 
>> 
>> 
>> -- 
>> 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
>