bound solution update in nonlinear solver

Question

For certain problem I find it useful to bound the solution update. Is there a way to do this using the PETScSNESSolver? After each iteration as like to do something like

 i = (dx > ub):
 dx[i] = ub
 i = (dx<lb)
 dx[i] = lb
 x -= dx

where x is my solution.

Answer 1

There are specialised solvers for bound-constrained problem. Look at this demo:

https://bitbucket.org/fenics-project/dolfin/src/f8a70425aef3c80c3a260013833ad1ddc7b6aaa0/demo/undocumented/contact-vi-tao/python/demo_contact-vi-tao.py?at=master&fileviewer=file-view-default