# Defining a variable as a distribution

To define a variable as an Analytica probability distribution, first select the variable and open either the variable’s Object window or the Attribute panel of the diagram with Definition selected from the Attribute dropdown menu.

To define the distribution:

1. Click the expr menu above the definition field and select Distribution.
2. The Object Finder dialog opens, showing the Distribution library.
3. Select the distribution you wish to use.
4. Enter the values for the parameters. You can use an expression or refer to other variables by name in the parameter fields.
5. Click OK to accept the distribution.

If the parameters of the distribution are single numbers, a button appears with the name of the distribution, indicating that the variable is defined as a distribution. To edit the parameters, click this button.

If the parameters of the distribution are complex expressions, the distribution displays as an expression. For example:

Normal((Price/Mpy)*Mpg, Mpg/10)

Entering a distribution as an expression

Alternatively, you can directly enter a distribution as an expression:

1. Set the cursor in the definition field and type in the distribution name and parameters, for example - Normal(.105, 0.015)
2. Press Alt-Enter or click the
button.

You can also paste a distribution from the Distribution library in the Definition menu (see Using a library).

You can edit a distribution as an expression, whether it was entered as a distribution from the Distribution library or as an expression, by selecting expr from the expr menu.