[petsc-users] Values of a column in a parallel matrix

[Jed Brown]

"Daralagodu Dattatreya Jois, Sathwik Bharadw" <sdaralagodudatta at wpi.edu>
writes:

>  I am using AIJ matrix to solve Laplace problem in finite element
>  framework. To apply Neumann boundary conditions I need to obtain
>  values of first and last few columns and subtract it with the
>  corresponding right hand side vector. I understand that
>  MatGetColumnVector and MatGetValues are not collective. Is there any
>  other alternative petsc calls to achieve this in parallel?

Inhomogeneous Neumann conditions are normally applied by integration
over the boundary.  But if you need a linear combination of some columns
of the matrix, that's a MatMult.
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