code: def ce_init(self):
          
          retval = 0.0; correct = 0; totalCount = 0
          for layer in self.layers:
              if layer.active:
                  if layer.type == 'Output':
                      layer.error = self.errorFunction(layer.target, layer.activation) 
                      totalCount += layer.size
                      retval += Numeric.add.reduce((layer.target - layer.activation) ** 2)
                      correct += Numeric.add.reduce(Numeric.fabs(layer.target - layer.activation) < self.tolerance)
                  elif (layer.type == 'Hidden'):
                      for i in range(layer.size): # do it this way so you don't break reference links
                          layer.error[i] = 0.0
          return (retval, correct, totalCount)
docs: Initializes error computation. Calculates error for output
          layers and initializes hidden layer error to zero.