Asserting Evidence

There are several ways SamIam allows a user to assert and retract evidence on variables in a Bayesian network. The simplest way to set an evidence value is by using the Evidence Tree view, which is the leftmost window that appears in SamIam when a network is open. The Evidence Tree contains a tree-style list of every node in each sub model of the network (in the case of networks defined in the Hugin .net file format, there will be only one sub model), sorted lexicographically according to node names, and divided according to an enumerated variable property you choose, for example, Genie diagnosis type. Expanding the tree branch of a node reveals tree leaves for each of its defined states. Single-clicking the mouse on one of these states asserts that the variable is in that state with probability 1. SamIam indicates such an assertion visually by highlighting the name of the variable in the tree, the name of the asserted state, and the border of the node icon in the network display, by default in the color red. To retract evidence that has been set on a variable, single-click the name of the asserted state. Evidence can also be set by using the Monitors.

By right-clicking the background of the Evidence Tree window with the mouse, the user can pop up a context menu that provides a few convenient ways to set evidence on multiple variables at once. The first menu item, Reset Evidence, will retract evidence on every asserted variable. The menu item Set Defaults pertains to Genie files only. Choosing this item will assert the default evidence on the variables in the network, if the user has defined such defaults using Genie.

The instantiation clipboard is a new feature of SamIam 2.2 that can make working with evidence more convenient. The instantiation clipboard, accessible through the Tools menu, is a place where the user can save an instantiation over an arbitrary number of discrete finite variables, and recall the instantiation later. The user can copy the currently set evidence to the clipboard, or copy the answer to a MAP or MPE query. Once he has copied a useful instantiation, the user can save it to a file and load it later.


Asserting Evidence; Options Menu
of the Evidence Tree Window