Matlab bouncing ball in box

Hey, guys I'm new to matlab and I'm working on making a script that will create a 20x20 box and have a ball bounce continously off the walls. The program will ask the user to input the magnitude of the velocity and the angle between the velocity vector and the x-axis. It will then calculate and plot the position of the ball in a graph window.

So far this is what I have. I have the ball bouncing off the right side correctly and the top as well. But the ball isn't traveling far enough to the left and down as well. Here is the code.

set(gca, 'XLim',[-10 10], 'YLim', [-10 10]);
cla
axis square
ball = animatedline('color' , 'r', 'Marker', 'o' , 'MarkerSize',12,'MarkerFaceColor','r');
hx0 = .05
hy0 = .05 / sqrt(2);
hx = hx0;
hy = hy0;
xl = 2 %.02
xr = 9.65
yb = xl;
yt = xr;
x = 1
y = 1
while 1 == 1
    if x < xl
        hx = hx0
    end
    if x > xr
        hx = -hx0;
    end
    if y < yb
        hy = hy0;
    end
    if y > yt
        hy = -hy0;
    end
    x = x + hx;
    y = y + hy;
    clearpoints(ball);
    addpoints(ball,x,y);
    drawnow;
    pause(.01)
end

Answer 1

[Geoff Hayes]

Dakota - your axes limits are set as

set(gca, 'XLim',[-10 10], 'YLim', [-10 10]);

but the limits you set in code for the box are different

xl = 2 %.02
xr = 9.65
yb = xl;
yt = xr;

I think that you can either reset the axes limits once you set the above four variables with

set(gca, 'XLim',[xl xr], 'YLim', [yb yt]);

or just set your limits to that of the axes

xl = -10;
xr = 10;
yb = xl;
yt = xr;

[Dakota Nielsen]

Thank you so much!

Answer 2

[Jan]

Your point starts at [1,1], but it changes the direction at this strange limits:

xl = 2; %.02
xr = 9.65;
yb = xl;
yt = xr;

A simplified version with adjusted limits:

axes('XLim',[-10 10], 'YLim', [-10 10], 'NextPlot', 'add');
axis square
hx = 0.05;
hy = 0.05 / sqrt(2);
xl = -9.65;
xr =  9.65;
yb = xl;
yt = xr;
x  = 1;
y  = 1;
for k = 1:5000 % while 1 == 1
    if x < xl || x > xr 
        hx = -hx;
    end
    if y < yb || y > yt
        hy = -hy;
    end
    x = x + hx;
    y = y + hy;
    plot(x,y, '.');
end

Answer 3

[Scott MacKenzie]

There are alternatives to animatedline. You can create a ball using rectangle with the curvature property set to 1. But, given the approach you are taking and the issue in your question -- the ball isn't traveling far enough to the left and down as well -- change

xl = 2;

to

xl = -10; % adjust as per marker width