Equation Contributions
You can add Equation Contributions () directly from the Global Definitions node and from the Definitions node under the Component (local) nodes. If Group by Type is active, the equation contribution nodes appear in the Equation Contributions () branch.
Many of the equation contribution nodes can also be added as auxiliary equation-based contributions under a physics interface. See About Auxiliary Equation-Based Nodes. In this case, the physics interface will contain a lightweight wrapper node that controls a hidden definitions node. The settings are therefore identical whether the node appears under a Definitions branch or in a physics interface.
When an equation contribution node which declares degrees of freedom is added under a physics interface, the physics interface controls whether the dependent variables are solved for or not in a study step. Degrees of freedom which are declared by nodes added directly under Global Definitions and component Definitions branches can be controlled individually in the Modify model configuration for study step tree in study step nodes.
To display the Equation Contribution node and its subnodes, click the Show More Options button () or select it from the Global Definitions or Definitions node’s context menu and select Equation-Based Contributions under Physics in the Show More Options dialog.
The following equation contribution nodes are available:
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 State Variables: for defining dependent variables that are updated using an update expression before or after each completed solver step. See State Variables.
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Global Dependent Variables: for declaring a number of named global dependent variables. See Global Dependent Variables.
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Global Weak Contribution: for adding a global weak expression to the overall system of equations. See Global Weak Contribution.
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Global Constraint: for constraining a global expression through elimination on the overall system of equations. See Global Constraint.
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Dependent Variable Field: for declaring a scalar or vector dependent variable field on a selection. See Dependent Variable Field.
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Weak Contribution: for adding a weak contribution integrated on a selection to the global system of equations. See Weak Contribution.
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Constraint: for constraining an expression on a selection. The constraint can be enforced by elimination, weakly or using a Nitsche penalty method. See Constraint.