.. index:: Requisite Parents

.. _Requisite_Parents:

Requisite Parents
=================

Not all available observations matter when a decision must be made. Intuitively, a parent of a decision node is said to be requisite if the value of the parent may affect the optimal choice of the decision.

The performance of inference in a LIMID can be improved, if the network is simplified by removing the nonrequisite parents of all decision nodes.

:ref:`Lauritzen and Nilsson (2001)<references>` present an algorithm for removing the nonrequisite parents of the decision nodes in a LIMID. The result of this algorithm is a LIMID, where no parent of a decision node is nonrequisite. This network is known as the minimal reduction of the LIMID.

Our definition of requisiteness is slightly different than the one given by Lauritzen and Nilsson: **We define a parent of a decision node to be requisite if and only if it is also a parent of the decision node in the minimal reduction of the LIMID.**

Inspect the requisite parents of a decision node
------------------------------------------------

Select a decision node. Click **Network -> Analysis -> Show requisite parents for decision.**

Requisite parents will be marked with a green V (see Figure 1) and non-requisite parents will be marked with a red X (see Figure 2).

.. figure:: images/requisiteparents.png

	Figure 1: Requisite parents are marked with a green V.

.. figure:: images/requisiteparents1.png

	Figure 2: Non-requisite parents are marked with a red X.

.. note:: If the model is a class, this function is only available in run-mode. If the model is a flat net, the function is available in both edit-mode and run-mode.