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Source Code for Module fuzzy.set.SFunction

  1  # -*- coding: utf-8 -*- 
  2  # 
  3  # Copyright (C) 2009  Rene Liebscher 
  4  # 
  5  # This program is free software; you can redistribute it and/or modify it under 
  6  # the terms of the GNU Lesser General Public License as published by the Free  
  7  # Software Foundation; either version 3 of the License, or (at your option) any 
  8  # later version. 
  9  # 
 10  # This program is distributed in the hope that it will be useful, but WITHOUT  
 11  # ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS 
 12  # FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more 
 13  # details. 
 14  #  
 15  # You should have received a copy of the GNU Lesser General Public License 
 16  # along with this program; if not, see <http://www.gnu.org/licenses/>.  
 17  # 
 18   
 19  """Realize a S-shaped fuzzy set.""" 
 20   
 21  __revision__ = "$Id: SFunction.py,v 1.19 2010-03-28 18:44:46 rliebscher Exp $" 
 22   
 23   
 24  from fuzzy.set.Function import Function 
 25   
 26 -class SFunction(Function): 
 27      r""" 
 28      Realize a S-shaped fuzzy set:: 
 29                   __ 
 30                  /| 
 31                 / | 
 32                /| | 
 33              _/ | | 
 34               | a | 
 35               |   | 
 36              2*delta 
 37   
 38      See also U{http://pyfuzzy.sourceforge.net/demo/set/SFunction.png} 
 39       
 40      @ivar a: center of set. 
 41      @type a: float 
 42      @ivar delta: absolute distance between x-values for minimum and maximum. 
 43      @type delta: float 
 44      """ 
 45   
 46 -    def __init__(self, a=0.0, delta=1.0): 
 47          """Initialize a S-shaped fuzzy set. 
 48   
 49          @param a: center of set 
 50          @type a: float 
 51          @param delta: absolute distance between x-values for minimum and maximum 
 52          @type delta: float 
 53          """ 
 54          super(SFunction, self).__init__() 
 55          self.a = a 
 56          self.delta = delta 
 57   
 58 -    def __call__(self, x): 
 59          """Return membership of x in this fuzzy set. 
 60             This method makes the set work like a function. 
 61              
 62             @param x: value for which the membership is to calculate 
 63             @type x: float 
 64             @return: membership 
 65             @rtype: float 
 66             """ 
 67          a = self.a 
 68          d = self.delta 
 69          if x <= a-d: 
 70              return 0.0 
 71          if x <= a: 
 72              t = (x-a+d)/(2.0*d) 
 73              return 2.0*t*t 
 74          if x <= a+d: 
 75              t = (a-x+d)/(2.0*d) 
 76              return 1.0-2.0*t*t 
 77          return 1.0 
 78   
 79 -    def getCOG(self): 
 80          """Return center of gravity.""" 
 81          from fuzzy.Exception import FuzzyException 
 82          raise FuzzyException("COG of SFunction uncalculable") 
 83   
 84 -    def getValuesX(self): 
 85          """Return sequence of x-values so we get a smooth function.""" 
 86          a = self.a 
 87          d = self.delta 
 88          stepsize = 2. * d / Function._resolution 
 89          x = a - d 
 90          for _ in range(Function._resolution): 
 91              yield x 
 92              x += stepsize 
 93          yield a + d 
 94   
 95 -    def __repr__(self): 
 96          """Return representation of instance. 
 97                      
 98             @return: representation of instance 
 99             @rtype: string 
100             """ 
101          return "%s.%s(a=%s, delta=%s)" % (self.__class__.__module__, self.__class__.__name__, self.a, self.delta) 
102   

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