[petsc-users] matrix preallocation for unstructured finite element

Sanjay Govindjee s_g at berkeley.edu
Thu Jan 18 22:59:14 CST 2018

If you are doing FEA, then you should have the element connectivity data 
available from the input.  From this it is an easy task to compute the 
the assembly pattern and hence the precise allocation data, dnz and 
onz.  There should be no need to perform a 'trial' assembly.


On 1/18/18 8:49 PM, saturday luis wrote:
> Hi PETSc team:
> Is there a way to make precise matrix preallocation for an 
> unstructured grid (I am not using the DMPlex object). Or do you have 
> any example code for estimating the dnz & onz data?
> On top of my head, I can do a two-phase calculation. I can first give 
> a rough estimate and do one finite element assembly, then I will call 
> MatGetRow to locate the column indices for nonzero entries. Then in 
> the second step, I will destroy the Mat and create a new Mat with this 
> obtained sparsity pattern.
> Do you have any suggestions?
> Thanks!
> Luis

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