If you zero the row and column as suggested, you can get what you want
by building the
RHS as you construct your matrix (i.e. do in while assembling your
matrix and RHS).
On 3/20/17 8:48 PM, Daralagodu Dattatreya Jois, Sathwik Bharadw wrote:
Hey Barry,
I am already using MatZeroRows. I was actually stuck precisely while
applying non zero Dirchlet boundary conditions. But to account for non
zero value traditionally we subtract the corresponding column with the
right hand side vector. If we zero the rows and columns we can only
have value zero for solutions at the boundary.
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------------------------------------------------------------------------
*From:* Barry Smith <[email protected]>
*Sent:* Monday, March 20, 2017 11:33:20 PM
*To:* Daralagodu Dattatreya Jois, Sathwik Bharadw
*Cc:* [email protected]
*Subject:* Re: [petsc-users] Values of a column in a parallel matrix
> On Mar 20, 2017, at 6:07 PM, Daralagodu Dattatreya Jois, Sathwik
Bharadw <[email protected]> wrote:
>
> Hey all,
>
> 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 andMatGetValues are not collective. Is there any
other alternative petsc calls to achieve this in parallel?
Hmm, I think you mean non-zero Dirichlet boundary conditions. In
that case the recommended approach is calling MatZeroRows() or if you
want to preserve symmetry MatZeroRowsColumns(). There are also
MatZeroRowsLocal() and MatZeroRowsColumnsLocal() and a few other variants.
Barry
>
> Thanks,
> Sathwik
