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Using Equations

Follow these steps to enter and use an equation to represent a node’s relationship with its parents:

1. Enter the equation into the node dialog box in the correct form, perhaps using built-in functions.  Here are some examples.

2. If the node is continuous, or has any continuous parents, they must be discretized.

3. Convert the equation to a table.

4. Use the net (e.g. compile it, do belief updating, absorb nodes, reverse links, or solve decision problems).  Netica will use the table generated from the equation.

If you change the equation for a node, or the discretization of the node or any of its parents, or the value of a relevant constant node, you must repeat step 3 above before the changes take effect.

Tips:

  If the equations get large, it may be easier to create them in a text editor, and then paste them into the node dialog box.

  When editing an equation you can cut, copy, paste, undo, etc. using their ctrl key commands, or by right-clicking.

  If there is a mistake in the syntax of the equation, Netica will pop up an alert box with an error message.  If necessary, move the alert box so that the equation is unobscured, and then click on the title bar of the Node Properties Dialog box.  That will cause the Node Properties to become the active window, and a selection point will appear in the equation text close to where the error is located.

  You can print out all the equations in the net, or select the nodes with equations.

  If you need to define intermediate variables to simplify the equations, implement them as new (intermediate) nodes.

  The tables generated by equations may result in large files (and therefore slow reading), so you may want remove the node’s table with Table Remove or  image\DelRelnTOOL.gif  before saving the net to file.  When you later read it in, do Table Equation to Table or  image\EqnToRelnTOOL.gif  (with no nodes selected) before using it.
 

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