How can I get matlab to draw lines between points?

Basically, I have to draw a pentagram. I've got the points, I just need the lines to be drawn between them. Here's my code so far:

axis equal

r = input('Enter the distance from the origin: ');
while r < 0
    r = input('The distance must be greater than 0: ');
end

angle = linspace(0,2*pi,6);
    x = r*sin(angle);
    y = r*cos(angle);
    plot(x(2),y(2),x(5),y(5),'or-',x(5),y(5),x(3),y(3),'or-',x(3),y(3),x(6),y(6),'or-',x(6),y(6),x(4),y(4),'or-',x(4),y(4),x(2),y(2),'or-')

I don't understand why adding the "-" part of 'or-' isn't making the lines show up.

Answer 1

[Akira Agata]

To draw pentagram, the latter half of your script should be:

angle = linspace(0,2*pi,6);
x = r*sin(angle);
y = r*cos(angle);
idx = mod((1:2:12), 5) + 1;
plot(x(idx),y(idx),'or-');

Answer 2

[Star Strider]

You’re overthinking the plot call.

Try this:

plot(x, y, 'or-')
axis([-1  1    -1  1]*2.1*r)
axis equal

[Benjamin Brown]

That's how I would do it if I wanted to make a pentagon, but I don't understand how to make the points go out of order to make a pentagram like this:

except without the circle around it.

[Star Strider]

Change the plot call to:

plot(x([1 3 5 2 4 1]), y([1 3 5 2 4 1]), 'or-')

That will work.