code: def prop_from(self, startLayers):
          
          if self.verbosity > 2: print("Partially propagating network:")
          # find all the layers involved in the propagation
          propagateLayers = []
          # propagateLayers should not include startLayers (no loops)
          for startLayer in startLayers:
              for layer in self.layers:
                  if self.path(startLayer, layer):
                      propagateLayers.append(layer)
          for layer in propagateLayers:
              if layer.active: 
                  layer.netinput = (layer.weight).copy() 
          for layer in propagateLayers:
              if layer.active:
                  for connection in self.connections:
                      if connection.active and connection.toLayer.name == layer.name:
                          connection.toLayer.netinput = connection.toLayer.netinput + \
                                                        Numeric.matrixmultiply(connection.fromLayer.activation,\
                                                                               connection.weight) # propagate!
                  if layer.type != 'Input':
                      layer.activation = self.activationFunction(layer.netinput)
          for layer in propagateLayers:
              if layer.log and layer.active:
                  layer.writeLog(self)
docs: Start propagation from the layers in the list
          startLayers. Make sure startLayers are initialized with the
          desired activations. NO ERROR CHECKING.