# Defining Named Distributions

You may define discrete chance nodes that use named distributions for their probability/value data. If you wish to use a named distribution for a discrete chance node, make sure you have not clicked the Separate Probability and Value Data Input Trees option in Node | Definition | General, because named distributions refer to probability/value pairs.

Rather than entering probability and value data directly, select a named distribution from the Distribution type drop-down box. The drop-down box contains the names of all named distributions supported by DPL (See Named Distributions).

To select a named distribution, click on the desired distribution from the drop-down box. DPL will put the distribution name in the probability data box and place the cursor ready for you to enter the first parameter.

An asterisk will appear in the value data box, indicating that DPL will calculate the value from the distribution. You only need to specify the distribution name once for each probability distribution required by the node. If the node requires separate probability distributions, they can be defined with different named distributions, or some can use named distributions and some can be directly specified. To specify probabilities directly, set the Distribution type box to (discrete) and enter the probabilities.

If you wish to specify the values for a named distribution (for example, you may want all the values to be integers), replace the asterisk with an appropriate data expression. If you specify values, you must do so for all values in the distribution. DPL will generate an appropriate probability for each value you enter. Note that DPL may not be able to generate probabilities based on the values you enter. Also, the resulting distributions will not represent the requested named distribution as accurately as if you allowed DPL to calculate the values.

After you select a distribution, an arc will appear across the branches of the corresponding node in the data tree, indicating that the probabilities and values will be generated from the named distribution.

* Versions:* DPL Professional, DPL Enterprise, DPL Portfolio

*See Also*