diff --git a/cellular_automata/nagel_schrekenberg.py b/cellular_automata/nagel_schrekenberg.py new file mode 100644 index 000000000000..be44761ecf82 --- /dev/null +++ b/cellular_automata/nagel_schrekenberg.py @@ -0,0 +1,140 @@ +""" +Simulate the evolution of a highway with only one road that is a loop. +The highway is divided in cells, each cell can have at most one car in it. +The highway is a loop so when a car comes to one end, it will come out on the other. +Each car is represented by its speed (from 0 to 5). + +Some information about speed: + -1 means that the cell on the highway is empty + 0 to 5 are the speed of the cars with 0 being the lowest and 5 the highest + +highway: list[int] Where every position and speed of every car will be stored +probability The probability that a driver will slow down +initial_speed The speed of the cars a the start +frequency How many cells there are between two cars at the start +max_speed The maximum speed a car can go to +number_of_cells How many cell are there in the highway +number_of_update How many times will the position be updated + +More information here: https://en.wikipedia.org/wiki/Nagel%E2%80%93Schreckenberg_model + +Examples for doctest: +>>> simulate(construct_highway(6, 3, 0), 2, 0, 2) +[[0, -1, -1, 0, -1, -1], [-1, 1, -1, -1, 1, -1], [-1, -1, 1, -1, -1, 1]] +>>> simulate(construct_highway(5, 2, -2), 3, 0, 2) +[[0, -1, 0, -1, 0], [0, -1, 0, -1, -1], [0, -1, -1, 1, -1], [-1, 1, -1, 0, -1]] +""" +from random import randint, random + + +def construct_highway( + number_of_cells: int, + frequency: int, + initial_speed: int, + random_frequency: bool = False, + random_speed: bool = False, + max_speed: int = 5, +) -> list: + """ + Build the highway following the parameters given + >>> construct_highway(10, 2, 6) + [[6, -1, 6, -1, 6, -1, 6, -1, 6, -1]] + >>> construct_highway(10, 10, 2) + [[2, -1, -1, -1, -1, -1, -1, -1, -1, -1]] + """ + + highway = [[-1] * number_of_cells] # Create a highway without any car + i = 0 + if initial_speed < 0: + initial_speed = 0 + while i < number_of_cells: + highway[0][i] = ( + randint(0, max_speed) if random_speed else initial_speed + ) # Place the cars + i += ( + randint(1, max_speed * 2) if random_frequency else frequency + ) # Arbitrary number, may need tuning + return highway + + +def get_distance(highway_now: list, car_index: int) -> int: + """ + Get the distance between a car (at index car_index) and the next car + >>> get_distance([6, -1, 6, -1, 6], 2) + 1 + >>> get_distance([2, -1, -1, -1, 3, 1, 0, 1, 3, 2], 0) + 3 + >>> get_distance([-1, -1, -1, -1, 2, -1, -1, -1, 3], -1) + 4 + """ + + distance = 0 + cells = highway_now[car_index + 1 :] + for cell in range(len(cells)): # May need a better name for this + if cells[cell] != -1: # If the cell is not empty then + return distance # we have the distance we wanted + distance += 1 + # Here if the car is near the end of the highway + return distance + get_distance(highway_now, -1) + + +def update(highway_now: list, probability: float, max_speed: int) -> list: + """ + Update the speed of the cars + >>> update([-1, -1, -1, -1, -1, 2, -1, -1, -1, -1, 3], 0.0, 5) + [-1, -1, -1, -1, -1, 3, -1, -1, -1, -1, 4] + >>> update([-1, -1, 2, -1, -1, -1, -1, 3], 0.0, 5) + [-1, -1, 3, -1, -1, -1, -1, 1] + """ + + number_of_cells = len(highway_now) + # Beforce calculations, the highway is empty + next_highway = [-1] * number_of_cells + + for car_index in range(number_of_cells): + if highway_now[car_index] != -1: + # Add 1 to the current speed of the car and cap the speed + next_highway[car_index] = min(highway_now[car_index] + 1, max_speed) + # Number of empty cell before the next car + dn = get_distance(highway_now, car_index) - 1 + # We can't have the car causing an accident + next_highway[car_index] = min(next_highway[car_index], dn) + if random() < probability: + # Randomly, a driver will slow down + next_highway[car_index] = max(next_highway[car_index] - 1, 0) + return next_highway + + +def simulate( + highway: list, number_of_update: int, probability: float, max_speed: int +) -> list: + """ + The main function, it will simulate the evolution of the highway + >>> simulate([[-1, 2, -1, -1, -1, 3]], 2, 0.0, 3) + [[-1, 2, -1, -1, -1, 3], [-1, -1, -1, 2, -1, 0], [1, -1, -1, 0, -1, -1]] + >>> simulate([[-1, 2, -1, 3]], 4, 0.0, 3) + [[-1, 2, -1, 3], [-1, 0, -1, 0], [-1, 0, -1, 0], [-1, 0, -1, 0], [-1, 0, -1, 0]] + """ + + number_of_cells = len(highway[0]) + + for i in range(number_of_update): + next_speeds_calculated = update(highway[i], probability, max_speed) + real_next_speeds = [-1] * number_of_cells + + for car_index in range(number_of_cells): + speed = next_speeds_calculated[car_index] + if speed != -1: + # Change the position based on the speed (with % to create the loop) + index = (car_index + speed) % number_of_cells + # Commit the change of position + real_next_speeds[index] = speed + highway.append(real_next_speeds) + + return highway + + +if __name__ == "__main__": + import doctest + + doctest.testmod()