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Page History: Fuzzy set approaches

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Page Revision: 2010/06/12 14:34


Fuzzy set approaches

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  • Fuzzy logic uses truth values between 0.0 and 1.0 to represent the degree of membership (such as using fuzzy membership graph)
  • Attribute values are converted to fuzzy values
    - e.g., income is mapped into the discrete categories {low, medium, high} with fuzzy values calculated
  • For a given new sample, more than one fuzzy value may apply
  • Each applicable rule contributes a vote for membership in the categories
  • Typically, the truth values for each predicted category are summed

Introduce

  • 컴퓨터를 인간에 가깝게 하는 일의 어려움
    - 퍼지 이론: 애매함을 처리하는 수리 이론

  • Fuzzy logic
    “X”가 “A”라는 집합 A(X)에 속하는 정도를 0과 1 사이의 숫자로 표현 예) μA(X)=0.7

  • Crisp logic
    - 전체 집합 X를 두 개의 Group, 즉 부분집합 A⊆X에 속하고 있는 요소와 속하고 있지 않는 요소에 이분하는 특성함수(characteristics function)에 의해 정의된다

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Principles of Fuzzy Set Theory

정의 1. 소속함수

전체 집합 Z의 부분집합 A에 대한 소속함수 μA(z)는 X로부터 폐구간 [ 0, 1 ]의 한 사상(Mapping)

μA : Z → [ 0, 1 ]

으로서, z가 A에 소속된 정도가 0 ≤μA(z) ≤1 값을 나타낸다. 이 때, z가 A에 완전히 소속된 경우 μA(z) = 1 (full membership)로 하고, 소속되지 않은 경우 μA(z) = 0 (no membership)으로 하며, z가 A에 소속된 정도가 부분적일 때 0 < μA(z) < 1 (Partial membership) 값을 갖도록 나타낸다.

정의 2. 퍼지집합

Z가 속한 임의의 원소 각각에 대해 어떤 특정한 성질을 갖는 정도를 나타내는 소속함수 μA(z), 즉 μA : Z → [0, 1]가 정의된다고 하자. 이 경우, 순서쌍의 집합 A = {(z, μA(x))|z∈ Z } 를 소속함수 μA(z)를 갖는 fuzzy set 이라고 한다.

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Operation

  • Empty : Membership function is identically zero in Z
  • Equality: Two fuzzy set A, B are equal (μA(z) = μB(z) for al z ∈ Z )
  • Subset : A fuzzy set A is subset of a fuzzy set B (μA(z) ≤ μB(z))
  • Complement, Union, Intersection

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Using Fuzzy Sets

  • R1 : IF the color is green THEN the fruit is Verdant OR
  • R2 : IF the color is yellow THEN the fruit is half-mature OR
  • R3 : IF the color is red THEN the fruit is mature

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  • General result involving two membership functions.
    - μ3(z,v) = min{μred(z), μmat(v)}

  • Fuzzy output due to rule R3 and specific input
    - Q3(v) = min{μred(z0), μ3(z0,v)}
    - Q2(v) = min{μyellow(z0), μ2(z0,v)}
    - Q1(v) = min{μgreen(z0), μ1(z0,v)}

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  • 집계 퍼지 출력 집계
    - Q = Q1 OR Q2 OR Q3
    - Q(v) = maxr{minss(z0),μr(z0,v)}}
    r = {1,2,3} , s={green, yellow, red}

  • Defuzzification
    - Obtain a crisp output v0 , from fuzzy set Q
    - Way to defuzzify Q to obtain a crisp output is “center of gravity”
    Q(1),Q(2)……Q(K)

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