Built-in functions : index function

index function

index(I)

Returns the index (instance number) of a member of a fixed membership or population submodel, for the level of submodel nesting specified by the argument.

Input: numeric

Result: numeric

Comment:

The index function is frequently used in conjunction with the element function when working with multiple-instance submodels: both fixed-membership and population submodels.

The argument specifies which index is to be returned. You can see summary information about the meanings of the different indices in the listbox headed Indices: in the equation dialogue. The argument is an integer between 1 and the maximum number of indices available. index(1) corresponds to the 'innermost' index, i.e., if you have one multiple-instance model inside another, the result of index(1) will be the index of the inner submodel instance, and the result of index(2) will be that of the outer submodel instance. Similarly, if a submodel has two dimensions, then index(1) and index(2) will be valid in that submodel, giving an instance's position along the inner and outer dimension respectively.

Relation submodels do not usually have indices of their own, but you can get the indices of their base submodel instances using the index() function. If one of the roles in a relation has been specified to 'allow base instance lookup', then the base submodel for this role will be 'innermost' and and the index of the instance in this role will be the result of calling 'index(1)' in the relation submodel.

For fixed-membership submodels, the function returns an integer value between 1 and n, where n is the number of instances for the submodel. For variable-membership submodels, it returns an integer between 1 and n, where n is the maximum possible index. For a population submodel this would be the total number of instances of the population that have ever existed during this simulation run. For a conditional submodel the maximum will be the size given in the submodel dimensions. For either of these, an instance with a particular index number may or may not exist.

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