Optional Method dependencies()

This optional method takes no arguments and returns a list of variable names that this variable needs in order to compute its values. Each variable name must be either an expression, a fully-qualified Opus variable name, or a dataset-qualified primary attribute name. It is important to list all dependent variables here and not invoke the computation of the dependent variables from the compute() method, since the dependencies tree mechanism would not work correctly (see Section 24.3.3). If the names of the dependent variables are not known at the time this method is called and are determined dynamically, the dependencies list can be extended from the compute() method using the Variable method add_and_solve_dependencies() which takes as arguments a list of additional dependencies (each specified either as a character string or an objects of class AttributeBox) and the dataset pool object. add_and_solve_dependencies() computes the additional variables and extends the dependencies list only when the compute() method runs for the first time.