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Fix bugs #13

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Fix bugs #13

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22 changes: 14 additions & 8 deletions ch06-swarm_intelligence-ants/carnival_aco.py
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Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,7 @@
# Set the probability of ants choosing a random attraction to visit (0.0 - 1.0)
RANDOM_ATTRACTION_FACTOR = 0.0
# Set the weight for pheromones on path for selection
ALPHA = 4
ALPHA = 5
# Set the weight for heuristic of path for selection
BETA = 7

Expand Down Expand Up @@ -52,7 +52,7 @@ def visit_attraction(self, pheromone_trails):
def visit_random_attraction(self):
all_attractions = set(range(0, ATTRACTION_COUNT))
possible_attractions = all_attractions - set(self.visited_attractions)
return random.randint(0, len(possible_attractions) - 1)
return possible_attractions.pop()

# Calculate probabilities of visiting adjacent unvisited attractions
def visit_probabilistic_attraction(self, pheromone_trails):
Expand All @@ -65,8 +65,8 @@ def visit_probabilistic_attraction(self, pheromone_trails):
for attraction in possible_attractions:
possible_indexes.append(attraction)
pheromones_on_path = math.pow(pheromone_trails[current_attraction][attraction], ALPHA)
heuristic_for_path = math.pow(1 / attraction_distances[current_attraction][attraction], BETA)
probability = pheromones_on_path * heuristic_for_path
heuristic_for_path = math.pow(20/ attraction_distances[current_attraction][attraction], BETA)
probability = pheromones_on_path + heuristic_for_path
possible_probabilities.append(probability)
total_probabilities += probability
possible_probabilities = [probability / total_probabilities for probability in possible_probabilities]
Expand All @@ -84,8 +84,9 @@ def roulette_wheel_selection(probabilities):
slices.append([possible_indexes[i], total, total + possible_probabilities[i]])
total += possible_probabilities[i]
spin = random.random()
result = [s[0] for s in slices if s[1] < spin <= s[2]]
return result[0]
for s in slices:
if s[1] < spin <= s[2]:
return s[0]

# Get the total distance travelled by this ant
def get_distance_travelled(self):
Expand Down Expand Up @@ -167,8 +168,13 @@ def update_pheromones(self, evaporation_rate):
for x in range(0, ATTRACTION_COUNT):
for y in range(0, ATTRACTION_COUNT):
self.pheromone_trails[x][y] = self.pheromone_trails[x][y] * evaporation_rate
for ant in self.ant_colony:
self.pheromone_trails[x][y] += 1 / ant.get_distance_travelled()

for ant in self.ant_colony:
distance = ant.get_distance_travelled()
for i in range(1, ATTRACTION_COUNT - 1):
x, y = ant.visited_attractions[i - 1], ant.visited_attractions[i]
self.pheromone_trails[x][y] += 1 / distance
self.pheromone_trails[y][x] += 1 / distance

# Tie everything together - this is the main loop
def solve(self, total_iterations, evaporation_rate):
Expand Down