Formulas are used to assign values to nodes or elements and to define the geometry of 3-D objects. The simplest formula is simply a numerical value such as "100." or "1.” In a new model, if the user selects Data|Edit Data Sets..., the Data Sets dialog box will appear and it can be seen that the default formulas for Kx is "100." This means that, in the absence of any other method (see Assigning Values to Data Sets) for assigning a value to an element, Kx for all elements will be 100. By using a slightly more complicated formula, it is possible to see the power of formulas. Here is an example:
•In the tree control on the left select "Required|Hydrology|Kz"
•In the Default Formula box, type "Kx/100" (without the quotation marks).
In the absence of any other method for assigning a value of Kz to an element, Kz for all elements will be equal to the value of Kx for that element divided by 100. Now by specifying the spatial distribution of Kx, the spatial distribution of Kz is also specified.
If the user clicks the button labeled Edit Formula, the Formula Editor will appear. The Formula Editor can help set up complex formulas correctly. See the "Formula Editor" for more information.
When a Formula is applied to a data set or boundary condition in the Data Sets tab of the Object Properties dialog box, the formula will only be used for those nodes or elements that the object affects (see "Objects").
Formulas are, in essence, mathematical expressions that can be evaluated to produce real-numbers, integers, Boolean values, or text. A formula can include constants and any of the operators or functions described in the following two sections. A text constant must be enclosed in double quotes. Boolean constants must be either "True" or "False". Numeric values that do not have a decimal point and that are not expressed in engineering notation (such as 1E0) are considered integers. Other numeric values are real numbers. The period is always used as the decimal point in real numbers in formulas even on computers where the regional settings indicate that some other character is used as the decimal point. Integers are 32-bit values. Real numbers are double-precision values. Spaces, tabs, and line breaks in formulas are considered white space and are otherwise ignored. Loop constructs such as “while”, “for”, and “do” are not supported.
