Fuzzy sets: extension principle












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I am a little bit confused about fuzzy set theory extension principle description. Most sources define extension principle in a following way:



Suppose $f:Xto Y$ and fuzzy set $Ain X$ such that $A=sum_{xin X}frac{mu_{A}(x)}{x}=frac{mu_{A}(x_{1})}{x_{1}}+...+frac{mu_{A}(x_{n})}{x_{n}}$.



Then extension principle states that the image of A under the mapping f can be expressed as a fuzy set $B=f(A)=frac{mu_{A}(f(x_{1}))}{x_{1}}+...+frac{mu_{A}(f(x_{n}))}{x_{n}}$



My question is how could fuzzy set be defined as a sum of rational numbers devided by vector? So in my consciousness it contradicts definition of fuzzy sets as a set of ordered pairs $(x,mu_{A}(x)), xin X$.



Will be very gratefull for explaining this problem or providing another, more easy to understand definition of extension principle!










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    0












    $begingroup$


    I am a little bit confused about fuzzy set theory extension principle description. Most sources define extension principle in a following way:



    Suppose $f:Xto Y$ and fuzzy set $Ain X$ such that $A=sum_{xin X}frac{mu_{A}(x)}{x}=frac{mu_{A}(x_{1})}{x_{1}}+...+frac{mu_{A}(x_{n})}{x_{n}}$.



    Then extension principle states that the image of A under the mapping f can be expressed as a fuzy set $B=f(A)=frac{mu_{A}(f(x_{1}))}{x_{1}}+...+frac{mu_{A}(f(x_{n}))}{x_{n}}$



    My question is how could fuzzy set be defined as a sum of rational numbers devided by vector? So in my consciousness it contradicts definition of fuzzy sets as a set of ordered pairs $(x,mu_{A}(x)), xin X$.



    Will be very gratefull for explaining this problem or providing another, more easy to understand definition of extension principle!










    share|cite|improve this question











    $endgroup$















      0












      0








      0





      $begingroup$


      I am a little bit confused about fuzzy set theory extension principle description. Most sources define extension principle in a following way:



      Suppose $f:Xto Y$ and fuzzy set $Ain X$ such that $A=sum_{xin X}frac{mu_{A}(x)}{x}=frac{mu_{A}(x_{1})}{x_{1}}+...+frac{mu_{A}(x_{n})}{x_{n}}$.



      Then extension principle states that the image of A under the mapping f can be expressed as a fuzy set $B=f(A)=frac{mu_{A}(f(x_{1}))}{x_{1}}+...+frac{mu_{A}(f(x_{n}))}{x_{n}}$



      My question is how could fuzzy set be defined as a sum of rational numbers devided by vector? So in my consciousness it contradicts definition of fuzzy sets as a set of ordered pairs $(x,mu_{A}(x)), xin X$.



      Will be very gratefull for explaining this problem or providing another, more easy to understand definition of extension principle!










      share|cite|improve this question











      $endgroup$




      I am a little bit confused about fuzzy set theory extension principle description. Most sources define extension principle in a following way:



      Suppose $f:Xto Y$ and fuzzy set $Ain X$ such that $A=sum_{xin X}frac{mu_{A}(x)}{x}=frac{mu_{A}(x_{1})}{x_{1}}+...+frac{mu_{A}(x_{n})}{x_{n}}$.



      Then extension principle states that the image of A under the mapping f can be expressed as a fuzy set $B=f(A)=frac{mu_{A}(f(x_{1}))}{x_{1}}+...+frac{mu_{A}(f(x_{n}))}{x_{n}}$



      My question is how could fuzzy set be defined as a sum of rational numbers devided by vector? So in my consciousness it contradicts definition of fuzzy sets as a set of ordered pairs $(x,mu_{A}(x)), xin X$.



      Will be very gratefull for explaining this problem or providing another, more easy to understand definition of extension principle!







      fuzzy-logic fuzzy-set






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      edited Apr 10 '16 at 13:50









      Andrés E. Caicedo

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      65.5k8159250










      asked Apr 10 '16 at 10:31









      BogdanBogdan

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      709






















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          Klir & Folger [1] says that
          $B=f(A)=frac{μ(x_1)}{f(x_1)}+...+frac{μ(x_n)}{f(x_n)}$, that is, the extension principle applies maps that map a crisp set to another, to fuzzy sets, turning a fuzzy subset $A$ to a fuzzy subset $B$.



          If more than one element of $X$ is mapped by $f$ to the same element $y in Y$, then the maximum of the grades is chosen as grade for $y$ in $f(A)$.



          [1] Klir & Folger, Fuzzy Sets, Uncertainty and Information, 1988.






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            $begingroup$

            Klir & Folger [1] says that
            $B=f(A)=frac{μ(x_1)}{f(x_1)}+...+frac{μ(x_n)}{f(x_n)}$, that is, the extension principle applies maps that map a crisp set to another, to fuzzy sets, turning a fuzzy subset $A$ to a fuzzy subset $B$.



            If more than one element of $X$ is mapped by $f$ to the same element $y in Y$, then the maximum of the grades is chosen as grade for $y$ in $f(A)$.



            [1] Klir & Folger, Fuzzy Sets, Uncertainty and Information, 1988.






            share|cite|improve this answer











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              0












              $begingroup$

              Klir & Folger [1] says that
              $B=f(A)=frac{μ(x_1)}{f(x_1)}+...+frac{μ(x_n)}{f(x_n)}$, that is, the extension principle applies maps that map a crisp set to another, to fuzzy sets, turning a fuzzy subset $A$ to a fuzzy subset $B$.



              If more than one element of $X$ is mapped by $f$ to the same element $y in Y$, then the maximum of the grades is chosen as grade for $y$ in $f(A)$.



              [1] Klir & Folger, Fuzzy Sets, Uncertainty and Information, 1988.






              share|cite|improve this answer











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                $begingroup$

                Klir & Folger [1] says that
                $B=f(A)=frac{μ(x_1)}{f(x_1)}+...+frac{μ(x_n)}{f(x_n)}$, that is, the extension principle applies maps that map a crisp set to another, to fuzzy sets, turning a fuzzy subset $A$ to a fuzzy subset $B$.



                If more than one element of $X$ is mapped by $f$ to the same element $y in Y$, then the maximum of the grades is chosen as grade for $y$ in $f(A)$.



                [1] Klir & Folger, Fuzzy Sets, Uncertainty and Information, 1988.






                share|cite|improve this answer











                $endgroup$



                Klir & Folger [1] says that
                $B=f(A)=frac{μ(x_1)}{f(x_1)}+...+frac{μ(x_n)}{f(x_n)}$, that is, the extension principle applies maps that map a crisp set to another, to fuzzy sets, turning a fuzzy subset $A$ to a fuzzy subset $B$.



                If more than one element of $X$ is mapped by $f$ to the same element $y in Y$, then the maximum of the grades is chosen as grade for $y$ in $f(A)$.



                [1] Klir & Folger, Fuzzy Sets, Uncertainty and Information, 1988.







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                share|cite|improve this answer








                edited Aug 13 '16 at 12:44

























                answered Aug 4 '16 at 7:25









                GspiaGspia

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