[r-t] Lead-based methods [was: Poll on consecutive blows in the same position]

[Matthew Frye]

On 29 Dec 2014, at 21:58, Don Morrison <dfm at ringing.org> wrote:

> Giving it a try, anyway….

This looks good. You've clearly thought very thoroughly.

> * "A process for generating a sequence of" may be troublingly vague,
> though at root, that's it's job! If there's value in going forward I'm
> sure someone will come up with a better way of phrasing this.

I like the vagueness. I think it needs to be this vague so as not to be restrictive. It really doesn't matter how the changes are generated, merely that they are generated somehow.

> * I've deliberately avoided using meaningful names for the kinds of
> methods defined, instead substituting Greek letters. If this is
> thought worth pursuing, then these abstract labels should be replaced
> with something more descriptive. I didn't want to use descriptive
> names to start, though, as they can rather prejudice things
> prematurely. But in case it's not immediately clear, what I'm trying
> to model is

I agree that abstract letters are good for now; I personally wouldn't object to final decisions being written in such terms but I suspect many others wouldn't like it! I'll also need to find where the α key is on my keyboard...

> An α-method is a method that when applied two or more times starting
> with the same row always produces the same sequence of changes.
> 
> A β-method is an α-method that when applied to any of the N! possible
> starting rows always results in the same sequence of changes.

I like this. It is a nice succinct articulation of the difference (far better than I managed); it makes explicit that β ("lead-based") is a subset of α ("rule-based"), which is rather obvious when you think about it.

Is there any doubt over the fact that most ringing currently done (and all allowed by the CCCBR) is in the form of β-methods? Is it also clear that Dixon's Bob Minor is *not* a β-method? And even that MBD's St Simon/St Martin's example is not a β-method?

MF