TRAFFIC_SIMULATION
Simulate Traffic at a Light
function traffic ( cycle_num )
%*****************************************************************************80
%
%% TRAFFIC simulates the cars waiting at one traffic light.
%
%
%
% Parameters:
%
% Input, integer CYCLE_NUM, the number of 10-second time cycles to model.
%
% Local Parameters:
%
% Local, integer CARS, the number of cars waiting at the light.
%
% Local, integer CARS_IN, the total number of cars that have come.
%
% Local, integer CARS_OUT, the total number of cars that have left.
%
% Local, integer CYCLE, the number of time cycles that have elapsed.
%
% Local, integer CYCLE_LENGTH, the number of seconds in one time cycle.
%
% Local, integer GREEN_CYCLES, the number of 10-second time cycles that
% a green light lasts.
%
% Local, integer GREEN_TIMER, keeps track of the number of time cycles the
% green light has been on.
%
% Local, integer LIGHT, the state of the light.
% 'r', the light is now red.
% 'g', the light is now green.
%
% Local, real P, the probability that a new car will come to the light
% in the next second.
%
% Local, integer RED_CYCLES, the number of 10-second time cycles that
% a red light lasts.
%
% Local, integer RED_TIMER, keeps track of the number of time cycles the
% red light has been on.
%
%
% Initialize.
%
cars = 0;
cars_in = 0;
cars_out = 0;
car_wait_cycles = 0;
cycle = 0;
cycle_length = 10;
green_cycles = 2;
green_timer = 0;
light = 'r';
p = 0.3;
red_cycles = 4;
red_timer = 0;
%
% Set up the plot data.
%
plot_data = zeros(2,cycle_num+1);
%
% Handle the "0"-th cycle.
%
plot_data(1,cycle+1) = cycle;
plot_data(2,cycle+1) = cars;
prq ( cars, light, cycle );
%
% Handle cycles 1 through CYCLE_NUM.
%
for cycle = 1 : cycle_num
%
% Each second of the cycle, choose a random number.
% If it is less than P, then a new car appeared at the light at that second.
%
r = rand ( cycle_length, 1 );
cars_new = sum ( r < p );
cars = cars + cars_new;
cars_in = cars_in + cars_new;
%
% Handle this time cycle depending on whether the light is green or red.
%
if ( light == 'g' )
[ cars, cars_out, light, green_timer ] = go ( green_cycles, cars, ...
cars_out, light, green_timer );
else
[ cars, light, red_timer ] = stop ( red_cycles, cars, light, red_timer );
end
%
% At the end of this cycle, how many cars are waiting?
%
car_wait_cycles = car_wait_cycles + cars;
%
% Print the current status.
%
prq ( cars, light, cycle );
plot_data(1,cycle+1) = cycle;
plot_data(2,cycle+1) = cars;
end
plot ( plot_data(1,1:cycle_num+1), plot_data(2,1:cycle_num+1) )
xlabel ( 'Time Cycles' )
ylabel ( 'Cars Waiting' )
title ( 'Traffic waiting at a Light' )
fprintf ( 1, '\n' );
fprintf ( 1, ' Number of cycles = %d\n', cycle_num );
fprintf ( 1, ' Simulated time = %d seconds\n', cycle_num * cycle_length );
fprintf ( 1, ' Number of cars in = %d\n', cars_in );
fprintf ( 1, ' Number of cars waiting = %d\n', cars );
fprintf ( 1, ' Number of cars out = %d\n', cars_out );
fprintf ( 1, ' Percentage Out/In = %7.1f%%\n', 100 * cars_out / cars_in );
wait_average_seconds = car_wait_cycles * cycle_length / cars_in;
fprintf ( 1, ' Average wait = %7.2f seconds\n', wait_average_seconds );
wait_average_lights = car_wait_cycles / cars_in / ( red_cycles + green_cycles );
fprintf ( 1, ' Average wait = %7.2f light cycles\n', wait_average_lights );
return
end
function [ cars, cars_out, light, green_timer ] = go ( green_cycles, cars, ...
cars_out, light, green_timer )
%*****************************************************************************80
%
%% GO simulates traffic when the light is green.
%
%
%
% Parameters:
%
% Input, integer GREEN_CYCLES, the number of 10-second time cycles that
% a green light lasts.
%
% Input, integer CARS, the number of cars stopped at the light.
%
% Input, integer CARS_OUT, the total number of cars that have gone
% through the light.
%
% Input, integer LIGHT, the state of the light.
% 'r', the light is now red.
% 'g', the light is now green.
%
% Input, integer GREEN_TIMER, keeps track of the number of time cycles the
% green light has been on.
%
% Output, integer CARS, the number of cars stopped at the light.
%
% Output, integer CARS_OUT, the total number of cars that have gone
% through the light.
%
% Output, integer LIGHT, the state of the light.
% 'r', the light is now red.
% 'g', the light is now green.
%
% Output, integer GREEN_TIMER, keeps track of the number of time cycles the
% green light has been on.
%
%
% In one 10-second time cycle, we estimate 8 cars can move out.
%
cars_through = min ( 8, cars );
cars = cars - cars_through;
cars_out = cars_out + cars_through;
%
% Advance the timer. If the green light has timed out, reset the timer
% and switch to red.
%
green_timer = green_timer + 1;
if ( green_cycles <= green_timer )
light = 'r';
green_timer = 0;
end
return
end
function [ cars, light, red_timer ] = stop ( red_cycles, cars, light, ...
red_timer )
%*****************************************************************************80
%
%% STOP simulates the traffic when the light is red.
%
% Parameters:
%
% Input, integer RED_CYCLES, the number of 10-second time cycles that
% a red light lasts.
%
% Input, integer CARS, the number of cars stopped at the light.
%
% Input, integer LIGHT, the state of the light.
% 'r', the light is now red.
% 'g', the light is now green.
%
% Input, integer RED_TIMER, keeps track of the number of time cycles the
% red light has been on.
%
% Output, integer CARS, the number of cars stopped at the light.
%
% Output, integer LIGHT, the state of the light.
% 'r', the light is now red.
% 'g', the light is now green.
%
% Output, integer RED_TIMER, keeps track of the number of time cycles the
% red light has been on.
%
%
% Advance the timer.
% If the red light has timed out, reset the timer and switch to green.
%
red_timer = red_timer + 1;
if ( red_cycles <= red_timer )
light = 'g';
red_timer = 0;
end
return
end
function prq ( cars, light, cycle )
%*****************************************************************************80
%
%% PRQ prints the current traffic waiting at the light.
%
% Parameters:
%
% Input, integer CARS, the number of cars stopped at the light.
%
% Input, integer LIGHT, the state of the light.
% 'r', the light is now red.
% 'g', the light is now green.
%
% Input, integer CYCLE, the current 10-second time cycle.
%
fprintf ( 1, '%4d ', cycle );
if ( light == 'r' )
fprintf ( 'R ' );
else
fprintf ( 'G ' );
end
i = cars;
c = floor ( i / 100 );
i = i - 100 * c;
for j = 1 : c
fprintf ( 'C' );
end
x = floor ( i / 10 );
i = i - 10 * x;
for j = 1 : x
fprintf ( 'X' );
end
for j = 1 : i
fprintf ( 'I' );
end
fprintf ( 1, '\n' );
return
end
