The data sets, global variables, and functions that can be included in a formula are listed in the List of Data Sets, Global Variables, and Functions on the right in the Formula Editor. For compactness, they are shown in a tree view. To see the available data sets, global variables, or functions click the plus (+) sign to the left of Data Sets, Global Variables, or Functions to expand the list. Within functions, there are additional lists that can be expanded by clicking the plus sign to their left. When the terminal branches of the tree are visible, the user can double click on one of them to insert it into the formula at the location of the cursor. If any text in the formula is selected, it will be replaced by the data set or formula. See Functions for more information on the meanings of the functions.
Not all data sets will be listed in the data set list, because not all data sets can be included in a formula for all other data sets. For instance, a formula for a data set cannot include a reference to itself either directly or indirectly. For example, if the formula for Ky is "Kx," the formula for Kx could not include Ky because that would make the formula for Kx depend on itself. Another example of a circular reference that is not allowed is to set the formula for Ky to "Kx," the formula for Kz to "Ky," and the formula for Kx to "Kz." Because Kx ultimately refers back to itself, this circular reference is not allowed.
Another requirement for a data set to be included in a formula is that the data set used in the formula must be evaluated at the same locations as the data set or object for which the formula is being set up. For example, Kz can include a reference to Kx because both Kx and Kz are evaluated at elements; however, Kz cannot include a reference to Initial_Head (in PHAST models) because Kz is evaluated at elements and Initial_Head is evaluated at nodes.
Finally, the formula for a two-dimensional data set can only include a reference to two-dimensional data sets with the same orientation; however, the formula for three-dimensional data sets can include a reference to a two-dimensional data set of any orientation.
