class PiFunction(Function):
r"""
Realize a Pi-shaped fuzzy set::
_
/|\
/ | \
_/ | \_
| a |
| |
delta
See also U{http://pyfuzzy.sourceforge.net/demo/set/PiFunction.png}
@ivar a: center of set.
@type a: float
@ivar delta: absolute distance between x-values for minimum and maximum.
@type delta: float
"""
def __init__(self, a=0.0, delta=1.0):
"""Initialize a Pi-shaped fuzzy set.
@param a: center of set
@type a: float
@param delta: absolute distance between x-values for minimum and maximum
@type delta: float
"""
super(PiFunction, self).__init__()
self.a = a
self.delta = delta
self._sfunction = SFunction(a - delta/2., delta/2)
self._zfunction = ZFunction(a + delta/2., delta/2)
def __call__(self, x):
"""Return membership of x in this fuzzy set.
This method makes the set work like a function.
@param x: value for which the membership is to calculate
@type x: float
@return: membership
@rtype: float
"""
if x < self.a:
return self._sfunction(x)
else:
return self._zfunction(x)
def getCOG(self):
"""Return center of gravity."""
return self.a
def getValuesX(self):
"""Return sequence of x-values so we get a smooth function."""
for x in self._sfunction.getValuesX():
yield x
# first value is equal the last of the previous sequence
skippedFirst = False
for x in self._zfunction.getValuesX():
if not skippedFirst:
skippedFirst = True
else:
yield x
def __repr__(self):
"""Return representation of instance.
@return: representation of instance
@rtype: string
"""
return "%s.%s(a=%s, delta=%s)" % (self.__class__.__module__, self.__class__.__name__, self.a, self.delta)
