Solving particle on a circle
BARTON ZWIEBACH: --that has served, also, our first example of solving the Schrodinger equation. Last time, I showed you a particle in a circle. And we wrote the wave function. And we said, OK, let's see what is the momentum of it. But now, let's solve, completely, this problem. So we have the particle in the circle. Which means particle moving here. And this is the coordinate x. And x goes from 0 to L. And we think of this point and that point, identify. We actually write this as, x is the same as x plus L. This is a strange way of saying things, but it's actually very practical. Here is 2L, 3L. We say that any point is the same as the point at which you add L. So the circle is the whole, infinite line with this identification, because every point here, for example, is the same as this point. And this point is the same as that point. So at the end of everything, it's equivalent to this piece, where L is equivalent to 0. It's almost like if I was walki...