[petsc-dev] controlling vector values while doing matrix free operations

[Matthew Knepley]

On Wed, Dec 14, 2011 at 4:07 PM, Philip, Bobby <philipb at ornl.gov> wrote:

> Hi:
>
> When doing the following operation in PETSc using FD approximations to a
>  Jacobian vector product
>
> J'(u)*a = [J(u+h*a) - J(u)]/h
>

Usually, we would put in F where you have J.


> is there a way for the user to specify that the entries of u+h*a cannot be
> negative for example?
> Browsing the PETSc documentation it was not obvious whether I could do
> this.
>

You can do whatever you want in your F function, but you should really
investigate SNESVI if
you have bounds on your variables.

  Thanks,

     Matt


> Thanks,
> Bobby




-- 
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
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