Nonlinear Solvers

Linear Solvers in Sundance

As with linear solvers, Sundance has no built-in nonlinear solvers; it uses Trilinos solvers. The Trilinos nonlinear solver package is NOX.

A NOX solver can be constructed in a number of ways:

• Construct a NOX solver from a specification given in an XML file.
• Construct a NOX solver from ParameterList objects built in your source code.
• Construct NOX solver objects directly.

This document describes only the first of these methods.

Building NOX Solvers from XML

A NOX solver is constructed heirarchically out of lower-level objects such as line search algorithms, linear solvers, and convergence tests. The XML specification of a NOX solver reflects this heirarchical structure; the XML for a NOX solver contains subblocks for the line search, convergence test, and linear solver. The skeleton of a NOX solver specification looks like this:

<ParameterList name="NOX Solver">

   <!-- solver type information goes here -->

   <ParameterList name="Line Search">
      <!-- line search parameters go here -->
   </ParameterList>

   <ParameterList name="Status Test">
      <!-- convergence checking parameters go here -->
   </ParameterList>

   <ParameterList name="Linear Solver">
      <!-- Linear solver parameters go here -->
   </ParameterList>

</ParameterList>

The "Linear Solver" block simply contains the XML to specify a linear solver, as described in Linear Solvers.

Most parameters from an XML file are mapped directly into NOX parameter objects. See the NOX parameter documentation for information on available parameters.