class ACO(object):
def __init__(self, bins, items, population, evaporation, limit=10000):
self.bins = bins
self.items = items
self.ants = []
for i in range(population):
self.ants.append(Ant())
self.graph = Graph(len(bins), len(items))
self.evaporation = evaporation
self.limit = limit
self.numOfEvaluations = 0
self.ran = False
self.runtime = 0
self.bestRun = None
self.avgFitness = []
def run(self):
"""Runs a full ACO run."""
self.ran = False
self.bestFits = []
self.avgFitness = []
startTime = time()
while self.numOfEvaluations < self.limit:
self.explore()
for ant in self.ants:
if self.bestRun and ant.fitness < self.bestRun.fitness:
self.bestRun = ant.copy()
elif not self.bestRun:
self.bestRun = ant.copy()
self.ran = True
self.runtime = time() - startTime
def explore(self):
"""Create a route for all ants and evaporate the graph."""
self.ants = [*map(self.createPath, self.ants)]
best = None
for ant in self.ants:
ant.distributePheromones(self.graph)
fitnesses = [ant.fitness for ant in self.ants]
self.bestFits.append(min(fitnesses) / sum(self.items))
self.avgFitness.append(sum(fitnesses) / len(fitnesses))
self.graph.evaporate(self.evaporation)
def createPath(self, ant):
"""Reset the bins and create a route for the given ant.
:param ant: ant object
:returns: ant with new path
"""
for b in self.bins:
b.empty()
currentBin = 0
ant.route = []
for item in enumerate(self.items):
currentBin, item = self.nextBin(currentBin, item)
ant.route.append((currentBin, item))
ant.fitness = self.getCurrentFitness()
ant.bins = self.bins.copy()
self.numOfEvaluations += 1
return ant
def nextBin(self, currentBin, item):
"""Get the index of the next bin to place the item in.
:param currentBin: index of the current bin
:param item: item weight
:returns: next bin index
"""
column = self.graph.graph[currentBin][item[0]].tolist()
total = sum(column)
threshold = total * random()
current = 0.0
for index, weight in enumerate(column):
if current + weight >= threshold:
self.bins[index].addItem(item[1])
return index, item[0]
current += weight
def getCurrentFitness(self):
"""Calculate the fitness of the current bin configuration.
:returns: current fitness
"""
maxWeight = self.bins[0].totalWeight
minWeight = self.bins[0].totalWeight
for b in self.bins:
if b.totalWeight > maxWeight:
maxWeight = b.totalWeight
if b.totalWeight < minWeight:
minWeight = b.totalWeight
return maxWeight - minWeight
