Ultra-simple periodic scale definition for non-extended UDP notation

Gene and I are editing over each other on the wiki, and not on
purpose. I'm afraid I'm going to confuse him terribly, because he's
got like 6 posts of mine to respond to on XA, the huge extended UDP
notation post I wrote earlier, a post on the wiki, and some other
posts to respond to.

This is the simplest possible definition for UDP notation which uses
periodic scales, and doesn't handle any hip extended rootless scale
stuff:

Given a periodic scale S with period S[p], let the tonic be S[0] = 0.
If S is MOS, then let the generator S[m] = g such that g is the larger
specific interval in its generic interval class.

For any such S, there are two associated values u and d, called the
number of generators located "up" and "down" from the tonic. Let u be
the maximum integer such that S[m*u] = g*u, and 0 <= u < p. Likewise,
let d be the maximum integer such that S[-m*d] = -g*d, and 0 <= d < p.

Let U = uP, and D = dP. The UDP notation for a given mode of an MOS is
U|D(P). If P=1 we may omit it and just write U|D.

-Mike