Method reducefactor

libpgm/tablecpdfactor.py:214–254

Reduce the factor knowing that *vertex* equals *value*. Reducing the factor means erasing all possibilities for *vertex* other than *value* from the distribution, and removing *vertex* from the scope. Arguments: 1. *vertex* -- The UUID of the variable whose outc

(self, vertex, value)

        del(self.stride[vertex])
        
    def reducefactor(self, vertex, value):
        '''
        Reduce the factor knowing that *vertex* equals *value*. Reducing the factor means erasing all possibilities for *vertex* other than *value* from the distribution, and removing *vertex* from the scope.
        
        Arguments:
            1. *vertex* -- The UUID of the variable whose outcome is known.
            2. *value* -- The known outcome of that variable.
        
        Attributes modified: 
            *vals*, *scope*, *stride*, *card* -- Modified to reflect the data of the reduced factor.

        '''
        vscope = self.scope.index(vertex)
        vstride = self.stride[vertex]
        vcard = self.card[vscope]
        result = [0 for i in range(len(self.vals)/self.card[vscope])]
        
        # added step: find value index from evidence
        try:
            index = self.inputbn.Vdata[vertex]['vals'].index(value)
        except:
            raise Exception, "Second arg was not a possible value of first arg."
     
        # machinery that calculates values in summed out factor
        k = 0
        lcardproduct = 1
        for i in range(vscope):
            lcardproduct *= self.card[i]
        for i in range(len(result)):
            result[i] += self.vals[k + (vstride * index)]
            k += 1
            if (k % lcardproduct == 0):
                k += (lcardproduct * (vcard - 1))
        self.vals = result
        
        # modify scope, card, and stride in new factor
        self.scope.remove(vertex)
        del(self.card[vscope])
        for i in range(vscope, len(self.stride)-1):
            self.stride[self.scope[i]] /= vcard
        del(self.stride[vertex])
    
    def copy(self):
        '''Return a copy of the factor.'''