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NORSYS SOFTWARE © 2002 | NETICA API | C   VERSION   2.15  |
double MutualInfo_bn ( | sensv_bn* sens, const node_bn* Fnode ) |
Measures the mutual information between two nodes, which is how much a finding at one node (called the "findings node") is expected to alter the beliefs (measured as decrease in its entropy) at another node (called the "query node").
The query node is set by the particular sensv_bn created (see NewSensvToFinding_bn). The findings node is passed as Fnode.
This function returns the mutual information between two nodes (measured in bits). It can be used with any discrete or discretized nodes. Mutual information is the expected reduction in entropy of one node (measured in bits) due to a finding at another.
The maximum possible decrease in entropy of the query node is when entropy goes to zero, i.e. all uncertainty is removed. That happens when a finding is obtained for the query node. So to find the entropy of a node, measure the mutual information between a node and itself (that is why "entropy" is sometimes called "self information").
To create a sensv_bn that can measure mutual information, pass ENTROPY_SENSV for what_find when calling NewSensvToFinding_bn. For its Fnodes argument, pass a list of all the nodes that might later be passed as Fnode to this function.
Mutual information is symmetric between nodes (i.e. has the same value when finding and query nodes are reversed). That makes this function useful to measure the degree to which one findings node can effect a number of different query nodes in an efficient way, by just passing the findings node to NewSensvToFinding_bn, and each of the query nodes to this function.
This function is available as "Network -> Sensitivity to Finding" in Netica Application. For more information on it, contact Norsys for the "Sensitivity" document.
Version:
See also:
VarianceOfReal_bn | Use a different measure of sensitivity: variance reduction | |
NewSensvToFinding_bn | Create a new sensv_bn to measure mutual information |
Example:
See NewSensvToFinding_bn.