View source for Defining a variable as a distribution

[[Category:Analytica User Guide]]
[[Category: Variables]]
[[Category: Definitions]]
<breadcrumbs>Analytica User Guide > Expressing Uncertainty > {{PAGENAME}}</breadcrumbs>


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:
# Click the [[expr]] menu above the definition field and select '''Distribution'''.
#:[[File:Menu.png]]
# The [[Object Finder dialog]] opens, showing the Distribution library.
#:[[File:Distribution library.png]]
# Select the distribution you wish to use.
# Enter the values for the parameters. You can use an expression or refer to other variables by name in the parameter fields.
# 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.

:[[File:Button.png]]

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

:<code>Normal((Price/Mpy)*Mpg, Mpg/10)</code>

'''Entering a distribution as an expression'''

Alternatively, you can directly enter a distribution as an expression:
# Set the cursor in the definition field and type in the distribution name and parameters, for example - ''[[Normal]](.105, 0.015)''
# Press ''Alt-Enter'' or click the[[File:checks.png|centre|18x18px]]button.

You can also paste a distribution from the Distribution library in the [[Definition menu]] (see [[User Libraries#Using a library | 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.

:[[File:Expression.png]]

== See Also ==
* [[How to Fit a Distribution to Data]]
* [[Choosing an appropriate distribution]]


<footer>Choosing an appropriate distribution / {{PAGENAME}} / Including a distribution in a definition </footer>