[petsc-users] A number of questions about DMDA with SNES and Quasi-Newton methods

[Matthew Knepley]

On Sun, Oct 29, 2017 at 5:15 PM, zakaryah . <zakaryah at gmail.com> wrote:

> Good point, Jed - I feel silly for missing this.
>
> Can I use -snes_type test -snes_test_display with the Jacobian generated
> from a DMComposite?  When I try, it looks like the finite difference
> Jacobian is missing all the elements in the row corresponding to the
> redundant variable, except the diagonal, which is wrong.
>

Well, this leads me to believe the residual function is wrong. What the FD
Jacobian does is just call the residual
twice with different solutions. Thus if the residual is different when you
perturb the redundant variable, you should
have Jacobian entries there.


> I'm not sure my code for setting the submatrices is correct.  I'm
> especially uncertain about the submatrix J_bh, where b is the redundant
> variable and h is the displacements.  This submatrix has only one row, and
> all of its columns are non-zero.  Can its values be set with
> MatSetValuesLocal, on all processors?
>
> Is there an example of manually coding a Jacobian with a DMRedundant?
>

I don't think so. We welcome contributions.

  Matt

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>
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