For an unsubscripted variable you only need a single equation to define the variable. With subscripts, however, it is sometimes desirable to have more than one equation. There is an Add Eq button in the Equation Editor that allows you to do this. In the text editor you simply enter a number of equations as in:
capacity utilization[toledo] = production *
fraction production to toledo / capacity[toledo] ~~|
capacity utilization[bismark] = production * (1 -
|fraction production to toledo) / capacity[bismark]|
|~ The fraction of capacity used.|
Normally all but the last equation are left with empty units and comment fields. If you enter more than one set of units or comment you will get a warning message and all but the first will be ignored.
In the above example both equations used the same variables, but in a different way. In general different equations for a variable may use different variables. The Causal Tracing functionality of Vensim looks at the causality for each individual subscript. For symbolic relationships such as those used for the Tree diagram and Sketch operations the union of all inputs over all equations is used when representing causes.
See Also: Exception Equations