Output Fuzzy Variable
Spark! currently only supports two defuzzification methods:
Center of Gravity
The Center of Gravity defuzzification method calculates the center of
gravity for the "filled" portions of the sets. The center
of gravity is the point at which the set would "balance". In
figure 1 below, each of the "filled" portions of the sets is balanced
on the black wedge. The green line shows the 'x' value for the center of
gravity.
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Figure 1 |
In Figure 2, the sets are combined as they would in a Spark! model. The
green line shows the COG for each set, but in the output variable, we're
concerned with the point at which the combination of the sets would balance.
This point is shown by the black wedge. The COG defuzzification method,
calculates the 'x' value for that point.
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Figure 2 |
Maxima
The Maxima defuzzification method isn't one you find in many of the fuzzy
logic "theory and application" books. It is simply the index of
the set with the highest degree of membership.
This method is used when you do not want a specific 'x' value but are
interested only in which output set is the "winner". For
example if you were using a Spark! model to decide which weapon a video game
"bad guy" should fire. An output value of 35.46 wouldn't help
much. You're interested in which "Set" was most active
("Pistol", "Cannon", "Nuke", etc.).
This defuzzification method can be used to create Fuzzy State Machines (FuSMs).
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