Using JMP • Formula Editor • Use Local Variables
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Use Local Variables
You can create and use temporary numeric variables in expressions. You can use ordinary local variables or you can use parameters, which are special types of local variables. Local variables exist only for the evaluation of the formula in which they are defined. They appear in formulas as bold italic terms.
Local variables are most often used with Assignment functions, which can assign expressions to local variables that are used in a complex equation. (For details, see Assignment Functions in Formula Functions Reference.) This technique can sometimes simplify building an equation and improve the efficiency of its evaluation.
To build a formula that references values found in local variables
Step 1: Create the Local Variable
1.
Open the Formula Editor by right-clicking a column name in the data table and selecting Formula.
2.
Select a box in the formula editing area by clicking it. (It is selected when there is a red outline around it.)
3.
Click the menu on the formula element browser and select Local Variables from the formula element browser menu.
4.
Click New Local Variable.
5.
Type a name for the local variable. By default, local variables have the names t0, t1, and so on, and have missing values.
6.
Assign a starting value, and click OK.
7.
(Optional) To copy, edit, or delete a local variable, right-click (Ctrl-click on the Macintosh) its name and select Copy, Edit, or Delete.
Step 2: Insert a Local Variable into a Formula
1.
Select a term in the formula editing area by clicking it. (It is selected when there is a red outline around it.)
2.
Click the local variable name in the Local Variables list. It appears in the formula as a bold italic term.
Note: Another way to create local variables is to use the button on the Formula Editor keypad, which automatically creates and displays local variables and places a semicolon after it. See Add Operators, for details.
See Use Local Variables in a Formula, for an example of referencing local variables in a formula.
Incorporate Parameters
Parameters are special types of local variables that are recognized as model parameters in some platforms, such as Nonlinear fitting. They can be used in formulas just as ordinary local variables can.
To view examples of parameters
1.
In the sample data folder that was installed when you installed JMP, open the Nonlinear Examples folder and then US Population.jmp.
2.
Right-click the column name x-formula and select Formula.
3.
Click the menu on the formula element browser and select Parameters.
Notes:
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After completing a nonlinear fit or after using the Reset button in the nonlinear control panel, the parameter’s value is the most recent value computed by the nonlinear platform.
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Each time the fitting algorithm takes a step, the updated parameter values are shown in the Nonlinear report.
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When you paste a formula with parameters into a column, the parameters are automatically created for that column unless it has existing parameters with the same names.
To build a formula that references values found in parameters
Step 1: Create the Parameter
1.
Open the Formula Editor by right-clicking a column name in the data table and selecting Formula.
2.
Make sure a term is selected (a red highlight is around it in the formula editing area) in the formula editing area.
3.
Click the menu on the formula element browser and select Parameters.
4.
Click New Parameter.
5.
Type a name for the parameter. By default, parameters have the names b0, b1, and so on, and have missing values.
6.
Assign a starting value. It is important to enter this value when using a parameter in a model for the nonlinear platform. After completing a nonlinear fit, the parameter’s value is the most recent value computed by the nonlinear platform.
7.
(Optional) To add several parameters (one for each level of a categorical variable, for example) at once, select Expand into categories, selecting column. Then select the column for which you want to expand the parameter.
8.
Click OK.
9.
(Optional) To copy, edit, or delete a parameter, right-click (Ctrl-click on the Macintosh) its name and select Copy, Edit, or Delete.
Step 2: Insert a Parameter into a Formula
1.
Select a term in the formula editing area by clicking it. (It is selected when there is a red outline around it.)
2.
Click the parameter name in the Parameters list. The parameter appears in the formula as bold type.