[petsc-users] Question on non-zero pattern

[Sanjay Govindjee]

Thanks.  I think I will just destroy and reallocat when the pattern 
changes since
filling with zeros will force me into a bit of awkward programming.

On 3/14/13 12:59 PM, Satish Balay wrote:
> Only if you did MatSetValues(val=0) for those extra locations - the
> subsequent assembly will be efficient.
>
> You can alway verify with -info
>
> Satish
>
> On Thu, 14 Mar 2013, Sanjay Govindjee wrote:
>
>> When I pre-allocated, I preallocated sufficient on and off and off processor
>> memory for
>> all possible non-zero patterns.  So I assume that there will not be any
>> mallocs necessary.
>> Or am I mis-understanding how the preallocation works?
>>
>> -sanjay
>>
>>
>>
>> On 3/14/13 12:52 PM, Satish Balay wrote:
>>> But you might have mallocs with the new nonzero structure. Its proably
>>> more efficient to destroy/create a new mat with the new structure.
>>>
>>> Satish
>>>
>>> On Thu, 14 Mar 2013, Sanjay Govindjee wrote:
>>>
>>>> Found my answer, use
>>>>
>>>>             call
>>>> MatSetOption(Kmat,MAT_NEW_NONZERO_LOCATIONS,PETSC_TRUE,ierr)
>>>>
>>>> after the MatAssemblyEnd( ).
>>>>
>>>>
>>>> On 3/14/13 11:28 AM, Sanjay Govindjee wrote:
>>>>> Is there a mechanism for resetting a matrix's non-zero pattern?
>>>>>
>>>>> In particular,  I have a preallocated a matrix, set the values, and
>>>>> assembled it.
>>>>> And used it to solve a problem.
>>>>>
>>>>> Now I would like to zero it, and reassemble it with a different non-zero
>>>>> pattern.
>>>>> Note the matrix has been preallocated so that it can accommodate both
>>>>> non-zero
>>>>> patterns.
>>>>>
>>>>> -sanjay
>>