[petsc-users] SNES function domain error

[Adrian Croucher]

hi

On 03/12/15 18:43, Barry Smith wrote:
>     I absolutely do NOT recommend doing variable switching with SNES. Our Newton solvers are not designed with variable switching in mind so you get these absurd limitations like needing SNESLINESEARCHBASIC
>
>     It would be great if someone who understood variable switching would either 1) contribute a Newton that supports variable switching to PETSc or 2) enhance the current SNESSolve_NewtonLS to support variable switching (I don't know which is easier).

I had resigned myself to not being able to use a line search, partly 
because the nonlinear solver in the TOUGH2 simulator (which we've used 
for many years to solve geothermal flow problems with phase changes and 
variable switching) doesn't use one either, and it generally works fine 
without one. Without the line search, SNES is doing much the same thing 
and doesn't seem to be upset by the variable switching either. It's only 
the error handling that's causing trouble.

But also I couldn't really see how a line search could be made to work 
with variable switching. When you switch variables, you're effectively 
doing a discontinuous leap into another part of the solution space. How 
can searching along a line between the old phase conditions and the new 
ones be made to make sense? Are there literature examples where people 
have done it?

Cheers, Adrian

-- 
Dr Adrian Croucher
Senior Research Fellow
Department of Engineering Science
University of Auckland, New Zealand
email: a.croucher at auckland.ac.nz
tel: +64 (0)9 923 84611