Package rdkit :: Package ML :: Package Neural :: Module ActFuncs

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# Source Code for Module rdkit.ML.Neural.ActFuncs

     1  #
     2  #  Copyright (C) 2000-2008  greg Landrum
     3  #
     4  """ Activation functions for neural network nodes
     5
     6  Activation functions should implement the following API:
     7
     8   - _Eval(input)_: returns the value of the function at a given point
     9
    10   - _Deriv(input)_: returns the derivative of the function at a given point
    11
    12  The current Backprop implementation also requires:
    13
    14   - _DerivFromVal(val)_: returns the derivative of the function when its
    15                          value is val
    16
    17  In all cases _input_ is a float as is the value returned.
    18
    19  """
    20  import math
    21
    22 -class ActFunc(object):
    23    """ "virtual base class" for activation functions
    24
    25    """
    26 -  def __call__(self,input):
    27      return self.Eval(input)
    28
    29
    30 -class Sigmoid(ActFunc):
    31    """ the standard sigmoidal function """
    32 -  def Eval(self,input):
    33      return 1./(1.+math.exp(-self.beta*input))
    34
    35 -  def Deriv(self,input):
    36      val = self.Eval(input)
    37      return self.beta * val * (1. - val)
    38
    39 -  def DerivFromVal(self,val):
    40      return self.beta * val * (1. - val)
    41
    42 -  def __init__(self,beta=1.):
    43      self.beta=beta
    44
    45 -class TanH(ActFunc):
    46    """ the standard hyperbolic tangent function """
    47 -  def Eval(self,input):
    48      v1 = math.exp(self.beta*input)
    49      v2 = math.exp(-self.beta*input)
    50      return (v1 - v2)/(v1 + v2)
    51
    52 -  def Deriv(self,input):
    53      val = self.Eval(input)
    54      return self.beta * (1 - val*val)
    55
    56 -  def DerivFromVal(self,val):
    57      return self.beta * (1 - val*val)
    58
    59 -  def __init__(self,beta=1.):
    60      self.beta = beta
    61