# 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

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