# Temporal Clone

When modeling a system that evolves over time (as a DBN), random variables at a given time instant typically depend on the state of the system at past time instants.

In order to specify time dependencies, temporal clones can be constructed for the regular nodes.

A temporal clone of a variable X represents X at the previous time instant. Links can then be added from temporal clones to the regular nodes. Thus, the temporal clones represent the “interface” between two successive time slices.

Figure 1: Temporal clone T_master and regular node master. T_master represents master from previous time slice.

## Create temporal clone

To create a temporal clone, select the master node that should be cloned, then right-click the master node and click Create temporal clone, finally click the network panel at the position where the temporal clone should be inserted.

## The Temporal Clone

The following list higligts the main charactaristica of temporal clones.

- Both discrete and continuous chance nodes can have temporal clones. In the case of a DBN with mixed nodes, there are restrictions on the compilation of the model.

- The links of the network must respect the natural flow of time. This means that temporal clones can only have other temporal clones as parents (not regular nodes).

- Discrete temporal clones can have tables and models. These tables are used to define the distribution over the temporal clones for the first time slice. For subsequent time slices, the temporal clones are replaced by the actual nodes in the previous time slice. Because links are allowed between temporal clones, any distribution can be specified.

- For discrete temporal clones, the category and attributes related to states cannot be changed directly. Changes must be performed through their temporal masters: Identical changes are then automatically performed for the clones.

- A temporal clone can be deleted. But if the temporal master of the clone is deleted, then the clone is also deleted.