Because fuzziness and vagueness are common
characteristics in many decision-making problems, good
decision-making models should be able to tolerate
vagueness or ambiguity [12]. Therefore, involving the
fuzziness in human decision making is necessary to avoid
misleading of uncertainty in models by using fuzzy set and
fuzzy logic. A fuzzy set is a collection of object is X denoted
generally by x is a set of ordered pairs, where ( x ) μ A is the
membership function of x in A that maps X to the
membership grade between 0 and 1 [13].
A {( x , ( x )) x X } = μ A Î
Fuzzy inference system (FIS) is a computing
framework based on the concept of fuzzy set theory, fuzzy
rules, and fuzzy reasoning [14]. FIS works by mapping from
a given input to an output using fuzzy logic as illustrated in
Figure 1. There are two well-known fuzzy inference system,
the Mamdani fuzzy model and the Sugeno fuzzy model. In
this paper we used the Mamdani Fuzzy inference system
because the output membership functions of a Sugeno fuzzy
model can only be either linear or constant [13].
The Mamdani Fuzzy Inference System works by using
the fuzzy operation of min and max to determine output. A
fuzzy rule in a Mamdani fuzzy model has the form [14].
If x1 is A1 and ….and xn is An then y is B
where A and B are the linguistic variable defined by fuzzy
sets of the universe of discourse X and Y respectively. The
if-part of the rule “x is A” is the set of facts called
“antecedent or promise”, while the then-part of the rule “y is
B” is a set of action called “consequent or conclusion” [14].
Figure 1. Fuzzy Inference System
In general, Mamdani FIS has four factors to produce the
outputs as follows:
1. Fuzzification
Fuzzification is the process converting a crisp input
variable into fuzzy membership functions.
2. Knowledge base
The knowledge base is the collection of fuzzy if-then
rules and facts. The knowledge bases typically consist of a
database and a rule-base. The basic function of the database
is to provide the necessary information and known facts to
be used in fuzzy reasoning.
3. Fuzzy inference engine
The fuzzy inference engine aims to generating fuzzy
conclusions from the knowledge base. The engine will take
the conclusion since the fuzzified inputs have been
determined by rule evaluation. Then, one fuzzy output
distribution will be properly produced by combining all
conclusions of each rule.
4. Defuzzification