You can chain an output parameter to an input parameter to allow an input to be driven directly from the current value of an output, provided that the chaining does not create a circular dependency.
To chain an output parameter to an input parameter:
1. To view the parameters, double-click the Parameters cell of a system or the Parameter Set bar
2. In the Outline pane, to the right of New input parameter, click the New name cell and type a name for the parameter.
3. Click the New expression cell and type either a constant value or expression for the parameter.
4. Update the project, system, or Parameters cell to register the changes and return the values of the output parameter. Note that an update operation can be lengthy, depending on the analysis details.
In the screenshot you can see how an expression is best to be defined.
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