%Joy Perkinson
%1.020 Recitation, 4/17/09

function carplume
%Current version of this program has a car that moves and leaves behind a
%plume of particles as it goes.

%Set system boundaries
Xmax = 120;
Xmin = 0;

%Set initial values
Vx = 0; %Wind speed
Vy = 0.2;
x = 0; %Initial car position
y = 0;
Vc = 0.3; %Car speed
emiss = 2; %Rate of dropping particles, must be an integer
dt = 1;

%Storing the droped particles
%[1stx 1sty, 2ndx 2ndy, 3rdx 3rdy,...]
particles = [x y];
t=0; %Time counter

while 1
    t = t+1; %Increment time counter
    x = x+Vc*dt;
    %Tell car to start over if it's passed 120
    if x>Xmax
        particles = []; %Clear array
        x = 0; %Move car back to start, y is still 0
    end
    %Emit particles
    for i = 1:emiss
        particles = [particles; x y];
    end
    %Make particles move randomly
    if size(particles) == [1 2]
        particles(1,1) = particles(1,1) + Vx*dt + (rand-0.5)*sqrt(3);
        particles(1,2) = particles(1,2) + Vy*dt + (rand-0.5)*sqrt(3);
    else
        for i=1:length(particles)
            particles(i,1) = particles(i,1) + Vx*dt + (rand-0.5)*sqrt(3);
            particles(i,2) = particles(i,2) + Vy*dt + (rand-0.5)*sqrt(3);
        end
    end
%     if t==5 %Decide whether to drop particle
%         particles = [particles; x1 y1; x2 y2];
%         t=0; %Reset time counter
%     end
    plot(x,y,'o',particles(:,1),particles(:,2),'.')
    axis([Xmin-20 Xmax+20 Xmin-20 Xmax-20])
    pause(0.01)
end