Source code for infpy.dbn.rbm

#
# Copyright John Reid 2007
#

import numpy.random
import numpy

def sigmoid( x ):
    return 1.0 / ( 1.0 + numpy.exp( -x ) )

class RBM( object ):
    """
    A restricted boltzman machine
    """

    def __init__( self, H, V ):
        """
        Initialise the restricted boltzman machine with H hidden units and V
        visible units
        """
        self.H = H
        self.V = V
        self.init_random()

    def init_random( self, scale = 1.0 ):
        """
        Randomly initialise the biases and weights
        """
        self.b = numpy.asmatrix( numpy.random.normal( loc = 0.0, scale = scale, size = self.H ) )
        self.c = numpy.asmatrix( numpy.random.normal( loc = 0.0, scale = scale, size = self.V ) )
        self.W = numpy.asmatrix( numpy.random.normal( loc = 0.0, scale = scale, size = (self.H, self.V) ) )

    def Q_h( self, v ):
        """
        Compute Q(h=1|v)
        """
        return sigmoid( - self.b - self.W * numpy.asmatrix( v ).T )

    def P_v( self, h ):
        """
        Compute P(v=1|h)
        """
        return sigmoid( - self.c - numpy.asmatrix( h ) * self.W  )

    def update(
            self,
            v
    ):
        """
        Update a restricted boltzman machine
        """
        Q_h = self.Q_h( v )
        h = Q_h > r.uniform( size = Q_h.shape )
        return h

if '__main__' == __name__:
    rbm = RBM( H = 2, V = 3 )
    v = numpy.ones( (5,3) )
    rbm.update( v )