def expand(self):
agent = self.moves.index(None)
position = self.positions[agent]
new_nodes = []
for neighbour in self.grid.valid_neighbours(position):
# Check if cell is occupied by moved agent
if neighbour in self.moves:
continue
# Check for crossing edges
move_edge = Edge(position, neighbour)
if any(move_edge.conflicts(edge) for edge in self.taken_edges):
continue
# Check for illegal moves, if given
if self.grid.is_move_illegal(self.cost, position, neighbour):
continue
# Check for new conflicts with other groups
new_conflicts = self.conflicts
if self.grid.is_move_conflicting(self.cost, position, neighbour):
new_conflicts += 1
new_moves = self.moves[:]
new_moves[agent] = neighbour
new_taken_edges = self.taken_edges[:]
new_taken_edges.append(move_edge)
# Check if this means a new waypoint is now visited for this agent
new_visited_waypoints = self.visited_waypoints
if self.grid.on_visitable_waypoint(agent, neighbour,
self.visited_waypoints[agent]):
new_visited_waypoints = [
ws.copy() for ws in new_visited_waypoints
]
new_visited_waypoints[agent].add(neighbour)
# Agents can wait at goal for no cost, unless they will move again
# in the future, so we need to keep track of this 'credit'
additional_cost = 1
new_goal_waits = self.goal_waits
if self.agent_done(agent):
additional_cost = 0
new_goal_waits = self.goal_waits[:]
new_goal_waits[agent] += 1
elif self.goal_waits[agent]:
additional_cost = self.goal_waits[agent] + 1
new_goal_waits = self.goal_waits[:]
new_goal_waits[agent] = 0
# Calculate the new heuristic by looking at the difference for
# only this agent
h_before = self.grid.heuristic(agent, position,
self.visited_waypoints[agent])
h_after = self.grid.heuristic(agent, neighbour,
new_visited_waypoints[agent])
h_difference = h_after - h_before
new_heuristic = self.heuristic + h_difference
new_node = Node(self.grid, self.positions, new_moves,
self.cost + additional_cost, new_goal_waits,
new_conflicts, new_taken_edges, self,
new_visited_waypoints, new_heuristic)
new_nodes.append(new_node)
return new_nodes
