View source for The domain attribute and discrete variables

[[Category:Analytica User Guide]]
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The domain attribute specifies the set of possible values for a variable. You rarely need to view or change a domain attribute explicitly. The most common reason to set the domain is for a variable defined as a custom discrete distribution, especially '''ProbTable'''. You can do this by editing it directly as an index in the '''[[Custom discrete probabilities#Probtable(): Probability Tables|probtable view]]''' , so you can usually ignore the information below. The rare case you need it is to specify a distribution as discrete, when Analytica would not otherwise figure it out — because it has non-integer numerical value.

By default, the domain type is '''Automatic''', meaning Analytica figures it out when it needs to. Usually, this is obvious (see previous section). For a discrete quantity, the domain can be a list of '''numbers''' or a list of '''labels'''. If the domain is '''continuous''', it means that any number is valid. 

'''Editing the domain:''' You can view and edit the domain like any other attribute of a variable, in the '''Attribute''' panel:

# Select the variable.
# Open the '''Attribute''' panel, and select '''Domain''' from the '''Attribute''' menu.
# Select the domain type from the popup menu.

[[File:Chapter15_6.png]]

'''The domain type:''' 
{| class="wikitable"
! Automatic 
| The default, meaning Analytica should figure it out.
|-
! Continuous 
| Each cell of the result is a real number. Lower and upper bounds may be optionally specified. There is also a semi-continuous variation in which the value must be between the indicated bounds or it may be zero. The semi-continuous variation must be entered as an ''Expression'', e.g., <code>Continuous(100K, 1M, orZero: True)</code>. When defined as continuous, uncertain variables are treated as continuous, whereas the other types are discrete.
|-
! Integer
| Each cell of the result in an integer, with lower and upper bounds optionally specified. Uncertain results are graphed as discrete numeric.The Optimizer searches for an integer solution.
|-
! Grouped Integer
| (Optimizer edition only) All scalar decision variables belonging to the same group must have a value between 1 and n, where n is the number of cells belonging to the same group, and all the values of each must be different.
|-
! Boolean
| Each cell of the result is 0 (False) or 1 (True) valued.
|-
! Discrete 
| Discrete but its values are unspecified. Influences how uncertain quantities are treated and in some cases, how graph axes are scaled by default.
|-
! Explicit Values 
| You specify a list of possible values. Within this option, you can also select whether these possible values are to be limited to be textual or numeric.
|-
! Copy From Index 
| You enter the name of an index variable, to use its values as the domain, or another variable to copy its domain values.
|-
! Expression 
| An arbitrary expression that computes the domain type, ranges and possible values. The expression should return with a call to one of the functions [[Continuous]](), [[Integer]](), [[GroupedInteger]](), or [[Discrete]](), or it can return a list of values. The expression can contain arbitrary logic and can use values from other variables in the model.
|}

'''Domain in the Object window:''' You can also view and edit the domain attribute in the '''Object''' window if you set it to do so in the Attributes dialog (see [[Managing attributes]])

[[File:Chapter15_7.png]]

<tip title="Tip">
The domain of a discrete variable should include all its possible values. If not, its probability mass function might sum to less than 1.
</Tip>

==See Also==
* [[Continuous]]()
* [[Integer]]()
* [[GroupedInteger]]()
* [[Discrete]]()


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