Choosing the Fitness Function
Number of Hits
 
For all classification problems, in order to be able to apply a particular fitness function, the learning algorithms APS 3.0 must convert the value returned by the evolved model into “1” or “0” using the 0/1 Rounding Threshold. If the value returned by the evolved model is equal to or greater than the rounding threshold, then the record is classified as “1”, “0” otherwise.

Thus, the 0/1 Rounding Threshold is an integral part of all fitness functions used for classification and must be appropriately set in the Settings Panel -> Fitness Function Tab.

The Number of Hits fitness function is very simple and highly efficient, and is based on the number of samples correctly classified.

More formally, the fitness fi of an individual program corresponds to the number of hits and is evaluated by the formula:

If h > C, then fi = h; else fi = 0

where h is the number of sample cases correctly evaluated (number of hits), and C is the number of samples in the class with more members (predominant class).

So, for this fitness function, maximum fitness fmax is given by:

fmax = n

where n is the number of fitness cases.
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