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operator

An operator is an object that produces contributions to a globally coupled nonlinear system of equations based on functions and fields in the mesh. Examples of operators include diffusion and bimolecular recombination.

operator operatorName [ -parameters parameterList ]
[ -sign +/-1 ]
[ -extraIntegrationOrder n ]
[ -useNodalQuadrature ] [ -useInteriorQuadrature ]

The available operators and their parameters are listed in section 3.2.

The default sign is +1.

-extraIntegrationOrder can be used to reduce or increase the order of the numerical integration used to evaluate the operator. Each operator estimates the optimal order needed based on the order of interpolation of the fields and functions it was given. Some functions, however, provide nonlinear mappings which do not have a finite polynomial series expansion. In these cases, the interpolation order estimate provided by the function may not be adequate for accurate integration.

-useNodalQuadrature and -useInteriorQuadrature allow the user to override the default quadrature used by operators. Reaction operators typically use nodal quadrature which amounts to pointwise evaluation at the nodes of field elements. Most other operators use interior quadrature, which uses an integration scheme appropriate to exactly integrate the fields or functions it is operating on. Steep gradients over an element lead to problems with reaction operators if they use interior quadrature, so it is recommended that -useNodalQuadrature be used for the interiorRHS operator if given a reactive term.

The operator command creates a new command and returns the name of this command. Currently, the new command is only used for instantiation of the object-oriented data structure describing the operator in the model. In the future, the created command may allow post-instantiation reconfiguration of the operator, such as to allow turning on tangents contributions for a final nonlinear solve.

Parameter lists are simply ordered lists of strings describing one of a Field, a Function, or a TCL variable name. The string for a Function is the value returned by a previous function command.


next up previous
Next: Future directions: Up: Model definition commands Previous: Future directions:

Dan Yergeau
Tue Jul 23 12:05:19 PDT 1996