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Scoping Parameters for Reactions, Rules, and Events

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Definition of Parameter Scope Using a Parameter in Events and Rules Changing the Scope of a Parameter

Definition of Parameter Scope

Parameters are quantities used to define the behavior of a modeled system. Parameters can either be constant or change over time. SimBiology parameters are generally used to define rate constants.

A SimBiology parameter is defined either globally at the model level or locally at the kinetic law level. Scope refers to this definition of the parameter at the model or kinetic law level.

• If the scope of the parameter is global in the model, it can be used by any event or rule, or by any reaction rate expression in the model.

• If the scope of the parameter is at the kinetic law level, it can be used only by the reaction rate expression for which it was defined.

If you create a new parameter in the Project Settings-Parameters pane, the scope is set by default to the model. When you create a new parameter to define a reaction rate equation in the Project Settings-Reactions pane's Kinetic Law tab, you can choose whether to assign the parameter locally to the kinetic law or globally to the model.

SimBiology parameters are resolved hierarchically:

• For reaction rate, the software hierarchically uses the value of the parameter at the kinetic law level first. If no such parameter is at the kinetic law level, the software looks for the parameter at the model level.

• If two parameters have the same name, one at the model level and the other at the kinetic law level, the software uses the value of the parameter at the kinetic law level for the reaction rate. The software uses the value of the parameter at the model level for any rules or events that reference the parameter.

Note   If you want to vary a parameter that is being referenced in a reaction rate equation, that parameter must have a unique name, and have scope at the model level.

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Using a Parameter in Events and Rules

When you want to refer to a parameter in an event or rule expression, or in more than one reaction rate equation, the parameter scope must be at the model level.

If you want to vary a parameter that is being referenced in a reaction rate equation, that parameter must have a unique name, and have scope at the model level. See Definition of Parameter Scope for more information.

Note   To vary a parameter with a rule or an event, clear the ConstantValue check box in the Project Settings-Parameters pane, Settings tab.

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Changing the Scope of a Parameter

When you want to refer to a parameter in an expression for a rule, or in more than one reaction rate equation, the parameter scope must be at the model level.

To change the scope of a parameter in the SimBiology desktop:

1. In the Project Explorer, click Parameters, to open the Parameters pane.

2. In the Parameters table, right-click a parameter row select Change Parameter Scope to change the scope of the selected parameter from kinetic law to model, or the reverse.

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Using Constant Amount and Boundary Condition for Species

Changing Model Component Values Using Rules

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