[petsc-users] Calculate only the diagonal elements for matrix matrix multiplications

[Barry Smith]

   Matrix A and B, sparse or dense, parallel or sequential? 


> On Jun 22, 2016, at 3:27 PM, ehsan sadrfaridpour <it.sadr at gmail.com> wrote:
> 
> Hi,
> I need the diagonal elements from result of multiplying matrix A, B together. 
> I can get by multiplying the 2 matrices and then call MatGetDiagonal.
> However, I only need the values on the diagonal and the rest of the elements are useless for me.
> As the size of matrices increase, I am afraid it affect the performance.
> 
> So, I am looking for another method that only calculates the diagonal of multiplication and not the rest of elements.
> If there is not such a method for matrix, how can I use the vector's operations to reach the same results?
> 
> 
> Best,
> Ehsan