Generating the diagram

 
Figure 3:  

The steps required to produce the influence diagram Figure 4 are shown in Figure 3 as follows.

• The BASE:  command is used to establish the collections and , each containing twelve quantities (the $ symbol is used as a wildcard).
• The GRID0:  command is used to specify node coordinates, size, and colour for the influence diagram. The command line is followed by seven rows of information, divided into columns, with each column corresponding to a different node. The information in each column is, respectively:
  1. The name of the element or base (collection) which the node is to represent.
  2. The x coordinate of the centre of the node. Coordinates are for the unit square, with (0,0) representing the bottom left position, and (1,1) the top right.
  3. The y coordinate of the centre of the node.
  4. The node radius. (A value of zero supplied here leads to [B/D] choosing a default radius which depends on screen resolution.)
  5. The node colour. For most implementations there will be at least 16 colours available, represented by the integers 0..15, representing white, black, and so forth. (See [16] for details.)
  6. The x coordinate of the centre of the text label associated with the node. Usually, the label is the same as the name of the element or collection represented by the node.
  7. The y coordinate of the centre of the text label associated with the node.

• The ARC:  command is used to specify that an arc should be drawn between two given nodes, the name of the source node (representing information) being given before the name of the destination node (the collection being adjusted). The integer supplied determines the kind of arc drawn; the simplest are:
  • 1 - a directed arc.
  • 3 - a labelled directed arc, with the label portraying various kinds of information flow.
  • 5 - an unlabelled directed arc, together with a path correlation.
  • 7 - a labelled directed arc, together with a path correlation indicator.
  Thus, in this example we specify that labelled directed arcs should be drawn from each information source (the two nodes Y, Z) to each node to be adjusted ( and G). The LOOK:  command with argument grid  can be used to review grid and arc specifications.
• The OPTION:  command is used with the influence  parameter to direct [B/D] to produce an influence diagram.
• The CONTROL:  command is used with the overwrite  control to direct [B/D] not to clear the graphics screen at the end of every adjustment. This allows the influence diagram to be constructed from a sequence of related and/or unrelated adjustments. (With the overwrite  control switched off, [B/D] waits for you to click on the graphics screen at the end of an adjustment, and any further adjustment will clear the graphics screen.)
• Finally, a sequence of the adjustment commands, ADJUST: , are given for each of and . For example, the first will direct [B/D] to perform the adjustment of the element A firstly by the collection Y, and then partially by the collection Z.