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

[Philip, Bobby]

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 

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.

Thanks,
Bobby