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We have deferred the description of the commands Set Evidence, Clear Evidence, Control Value, Set Focus and Clear Focus to the current section, which offers background information to Bayesian network algorithms. We reproduce the Node menu, which is to a large degree duplicated by the node pop-up menu, below:
Set Evidence submenu allows for setting the node state, which amounts to observation of that node state. The submenu is active only if there is one (and only one) node selected in the Graph View.
To select a state of the currently selected node, select this state on the submenu listing the states and release the mouse button. The state will have a check mark next to its name. The node will from that point on be marked with a corresponding icon, indicating that one of the states of this node (True or False) has been observed. To change the node back to the unobserved state, choose Clear Evidence from the Node menu. Setting evidence for a node can be accomplish in three other ways: (1) By choosing Set Evidence in the node context menu, which is similar to the Node menu, (2) double clicking on one of the state icons (T or F), or (3) pressing the letter T or F (for True and False) once the node has been selected.
Control Value submenu works precisely like the Set Evidence submenu but it stands for controlling rather than observing the value. Controlling means that the value has been set from outside. QGeNIe's implementation of controlling the value follows so called arc-cutting semantics, which means that the incoming arcs of the controlled node become inactive (nothing inside the model influences the node, as its value is set from outside). QGeNIe shows these inactive arcs as inactive by dimming them. See Controlling values for more information about this functionality.
Clear Evidence command (for controlled nodes, this command is called Release Value) is active only if there are nodes selected in the Graph View and at least one of these node has been previously observed (or controlled). Clear Evidence un-observes a state, i.e., it reverses the effect of the Set Evidence command. Release Value un-controls a state, i.e., it reverses the effect of the Control Value command. The check mark next to the state name will disappear. The status icon will be adjusted accordingly.
The Set Focus command is active only if there is exactly one node selected in the Graph View. It allows you to set the status of the selected node(s) to be the Focus. The node will from that point on be equipped with the Focus () status icon, indicating that the node is the focus of reasoning. This is important in the value of information and value of control calculations.
The Clear Focus command is active only if the node selected is the focus. Clear Focus reverses the effect of the Set Focus command. The Focus () status icon will disappear.