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