Source code for jmetal.problem.singleobjective.knapsack
import random
import numpy as np
from jmetal.core.problem import BinaryProblem
from jmetal.core.solution import BinarySolution
"""
.. module:: knapsack
:platform: Unix, Windows
:synopsis: Single Objective Knapsack problem
.. moduleauthor:: Alejandro Marrero <alu0100825008@ull.edu.es>
"""
[docs]
class Knapsack(BinaryProblem):
"""Class representing Knapsack Problem."""
def __init__(
self,
number_of_items: int = 50,
capacity: float = 1000,
weights: list = None,
profits: list = None,
from_file: bool = False,
filename: str = None,
):
super(Knapsack, self).__init__()
if from_file:
self.__read_from_file(filename)
else:
self.capacity = capacity
self.weights = weights
self.profits = profits
self.number_of_bits = number_of_items
self.obj_directions = [self.MAXIMIZE]
[docs]
def number_of_variables(self) -> int:
return 1
[docs]
def number_of_objectives(self) -> int:
return 1
[docs]
def number_of_constraints(self) -> int:
return 1
def __read_from_file(self, filename: str):
"""
This function reads a Knapsack Problem instance from a file.
It expects the following format:
num_of_items (dimension)
capacity of the knapsack
num_of_items-tuples of weight-profit
:param filename: File which describes the instance.
:type filename: str.
"""
if filename is None:
raise FileNotFoundError("Filename can not be None")
with open(filename) as file:
lines = file.readlines()
data = [line.split() for line in lines if len(line.split()) >= 1]
self.number_of_bits = int(data[0][0])
self.capacity = float(data[1][0])
weights_and_profits = np.asarray(data[2:], dtype=np.float32)
self.weights = weights_and_profits[:, 0]
self.profits = weights_and_profits[:, 1]
[docs]
def evaluate(self, solution: BinarySolution) -> BinarySolution:
total_profits = 0.0
total_weigths = 0.0
for index, bits in enumerate(solution.variables[0]):
if bits:
total_profits += self.profits[index]
total_weigths += self.weights[index]
if total_weigths > self.capacity:
total_profits = 0.0
solution.objectives[0] = -1.0 * total_profits
return solution
[docs]
def create_solution(self) -> BinarySolution:
new_solution = BinarySolution(
number_of_variables=self.number_of_variables(), number_of_objectives=self.number_of_objectives()
)
new_solution.variables[0] = [True if random.randint(0, 1) == 0 else False for _ in range(self.number_of_bits)]
return new_solution
[docs]
def name(self):
return "Knapsack"
