fill for matrix multiplication

[Manav Bhatia]

Hi,

   I am performing a matrix multiplication of two dense matrices with  
both MatMatMult and MatMatMultTranspose.
   What do I choose a fill factor as? According to the definition in  
the documentation: fiill = expected fill as ratio of nnz(C)/(nnz(A) +  
nnz(B)).
  So, If I have two full matrices A and B, I will get a full matrix  
as my result. Hence, the fill factor will be 0.5. However, both these  
methods give an error with a fill factor less than 1.0. Also, if I  
use PETSC_DFAULT as the fill argument, it agains results in an error  
since its value is -2.

Kindly help me with your advice here.

Thanks
Manav
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