Virtual Number of States
Virtual Number of States in BayesiaLab
In BayesiaLab, you can define so-called Virtual Number of States for nodes. The Virtual Number of States replaces the actual number of states of a node for computing the Minimum Description Length Score (MDL Score), which serves as the quality metric for evaluating candidate networks during structural learning.
Using a Virtual Number of States has a similar objective as setting Local Structural Coefficients. However, unlike the Local Structural Coefficients, the Virtual Number of States applies only to one part of the node's MDL Score computation.
By modifying the Virtual Number of States of a node, you can increase or decrease the number of parents that will be linked to that node during structural learning. For instance:
- A Virtual Number of States higher than the actual number of states would decrease the number of parents.
- A Virtual Number of States lower than the actual number of states would increase the number of parents.
However:
- The Virtual Number of States can never be lower than the minimum number of states of a node, which is 2.
- The Virtual Number of States must always be an integer.
Usage
There are multiple ways to edit the Virtual Number of States of nodes:
Using the Virtual Number of States Editor to Edit Values for Multiple Nodes:
- From the Main Menu, select Edit > Edit Virtual Number of States.
- Click on the background of the Graph Panel, then, from the Contextual Menu, select Edit Virtual Number of States.
- If the Virtual States indicator appears in the Status Bar, click on the icon.
Editing the Virtual Number of States for an Individual Node:
- Right-click on the node, then, from the Contextual Menu, select Properties > Virtual Number of States.
Once you set a Virtual Number of States on at least one node, the indicator icon appears in the Status Bar.
Furthermore, the nodes for which you set a Virtual Number of States are marked with a tag.