[petsc-users] SNES update solution vector

[zakaryah .]

Hi Bikash,

I agree with Barry.  If your function changes, quasi Newton methods build
up the approximation to the Jacobian from sequential evaluations of the
function.  If your Jacobian doesn't change too much when the boundary
conditions change, just keep the last approximation and update it with the
new function.  Otherwise I don't see what you want to do.

I don't think you need to call SNESGetSolution, you should be able to just
access the vector that you pass to SNESSolve.

On Nov 3, 2017 6:34 PM, "Bikash Kanungo" <bikash at umich.edu> wrote:

Hi Barry,

So for Newton solvers that would work by explicitly setting the boundary
conditions in my gradient(function) and Jacobian vectors. But in
quasi-Newton solvers where the Jacobian is built from a history of previous
Jacobians and current gradient vector, I can't enforce a new boundary
condition. I can change the current gradient vector appropriately but I
don't see a way handle the the Jacobian.

Thanks,
Bikash



On Fri, Nov 3, 2017 at 6:20 PM, Smith, Barry F. <bsmith at mcs.anl.gov> wrote:

>
>
>   You should not need to "tamper" with the solution process to achieve
> this.
>
>   I would just change how my FormFunction and FormJacobian behave to
> implement the different boundary conditions. Why would that not work?
>
>    Barry
>
> > On Nov 3, 2017, at 4:39 PM, Bikash Kanungo <bikash at umich.edu> wrote:
> >
> > Hi Matt,
> >
> > I want to update the Dirichlet boundary condition on the solution vector
> on-the-fly. One way to do it is to destroy the current snes solver and
> create a new one with the new Dirichlet boundary condition (which means
> setting a new solution vector with a different size, size  = # of
> non-Dirichlet rows). But is it possible to work with the current snes and
> instead enforce the new Dirichlet boundary condition on the current
> solution vector?
> >
> > Thanks,
> > Bikash
> >
> > On Fri, Nov 3, 2017 at 5:19 PM, Matthew Knepley <knepley at gmail.com>
> wrote:
> > What do you want to do to it?
> >
> >   Matt
> >
> > On Fri, Nov 3, 2017 at 5:14 PM, Bikash Kanungo <bikash at umich.edu> wrote:
> > Hi,
> >
> > I'm trying to solve a nonlinear problem using BFGS Quasi-Newton solver.
> I would like to tamper the solution vector x on-the-fly, based on some
> criterion. Is there a way to do so? Will SNESGetSolution(SNES snes, Vec *
> x) allow me to do so for each SNES iteration?
> >
> > Thanks,
> > Bikash
> >
> > --
> > Bikash S. Kanungo
> > PhD Student
> > Computational Materials Physics Group
> > Mechanical Engineering
> > University of Michigan
> >
> >
> >
> >
> > --
> > 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/
> >
> >
> >
> > --
> > Bikash S. Kanungo
> > PhD Student
> > Computational Materials Physics Group
> > Mechanical Engineering
> > University of Michigan
> >
>
>


-- 
Bikash S. Kanungo
PhD Student
Computational Materials Physics Group
Mechanical Engineering
University of Michigan
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