[r-t] Jump change notation

[Don Morrison]

On Wed, May 27, 2015 at 2:12 PM Chris02 <chris02 at shropshirelad.plus.com>
wrote:
> It did occur to me that swapping adjacent bells could be considered
> as a jump change of distance 1. (As opposed to the more normal ones
> which are distance 2.) So how about enhancing your Insert(x,y)
> routine so it could handle not only the bell doing the jump, but
> also the ones shuffling up/down. It could then be used to handle
> swapping adjacent bells. (eg. Insert(3,4) to swap 3rds and 4ths
> place bell.) It could also be called to put in 1st place if needed
> and last place if needed. This would keep all the setting of the
> permutation array and all the error checking in one fairly simple
> routine.

Unless I've misunderstood you, I believe that this is exactly what I am
doing. That's what the k±1,k stuff is in the main loop:

| for k from 1 to N-2
|    if b[k] = null
|     if k-1 not in b
|       insert(k-1, k)
|     else
|       insert(k+1, k)

And similarly in the stuff that does the implicit leading and lying.

And, in fact, the test in insert() does do all the error checking (at least
all of it once you get past the preliminary, mundane stuff like making sure
everything is of the right type and length and so on).

And if you perversely choose to notate X (in major) as

(12)(21)(34)(43)(56)(65)(78)(87)

or

(12)(34)(56)(78)

or any of the many other such possibilities it'll parse it just fine. And
similarly, I am using the same code to parse ordinary changes with places,
which are just a degenerate case of jump changes in Holroyd notation.

Or have I misunderstood your point?



-- 
Don Morrison <dfm at ringing.org>
"It is the present, not the past, that dies."
             -- Will Durant, _Fallen Leaves_
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