[r-t] 40320 Spliced Major (3m)

[Alexander Holroyd]

This sounds fascinating, Mark.  Are you going to show us the composition?
Ander

On Mon, 2 Jul 2012, Mark Davies wrote:

> Yes, it seems the desire to get an extent of spliced Plain and Helixoid Major 
> was the real motivation behind Philip's initial request for a list of all 
> Helixoids. It struck me as an interesting challenge. It is in my experience 
> rare to be asked for an extent of Major, and rarer still for there to be a 
> real danger of any resulting composition being rung!
>
> However, it quickly became obvious that the very different construction of 
> the two method types made the task pretty difficult. As Philip has pointed 
> out, it is easy to find a touch (3M) which puts the triplet (1,2,3) into 
> every possible position, just like the first three leads of the Helixoid, but 
> sadly this does not at all imply that the remaining five bells produce 
> changes which allow the two 336-row blocks to be spliced together. It's easy 
> enough to see why this might be: in the Helixoid, the triplet is treated 
> symmetrically, with (1,2,3) falling into every possible position up to 
> self-permutation within the half-lead. Successive half-leads simply run 
> through all the permutations of (123). By contrast, in a Plain method the 
> triplet is treated as a hierarchy of hunts, with the treble visiting every 
> place within a half-lead, then (12) filling every one of their positions in 
> the half-course, and finally the entire triplet completing the set only once 
> the full touch is complete.
>
> In fact, a little more thought showed that no Helixoid existed which could be 
> course-spliced with the 3M touch of Plain Bob. I set out my reasoning to 
> Philip as follows:
>
> 1. The PB8 touch certainly includes the plain course, so any
> course-spliced Helix method must also include these changes.
>
> 2. Immediately after the Wrong, the PB8 plain course contains change
> 31254768. Where can this occur in the Helix?
>
> 3. It must be a leadhead, since its prefix is a positive 3-cycle on
> (123), and all such are by definition leadheads in a
> (123)(45678)-Differential.
>
> 4. But now we have a contradiction: the suffix 54768 is not a leadhead
> in any method with a 1- or 5-cycle on (45678).
>
> A month went by with no real progress, until I chanced upon the idea that a 
> different touch of Plain Bob might work better. What it turned out I needed 
> was a block where the triplet (123) followed a fundamental rule of the 
> Helixoids: given arrangements of (123) always occur at the same place in the 
> Helixoid lead, and so have the same sign. Or more precisely, they have the 
> same sign if you rotate (123), but the opposite sign if you swap a pair from 
> (123), since that gives you a row in the second half-lead. If I could find a 
> touch of Plain Bob (or any plain method) where all positions of (123) 
> occurred, and all obeyed this rule of signs, then I reasoned it might become 
> possible to find course-splicing Helixoids.
>
> I soon found touches which obeyed this property, but *only* in methods where 
> the half-lead was a true plain hunt (that is, Plain Bob, Reverse Bob, Double 
> Bob and Plain Hunt itself) and *only* if I used special calls such as 1278 or 
> 123456. In fact, nothing else worked other than three full hunting courses in 
> the positive coursing orders 32....., 3..2... and 3....2. or their negative 
> reverses. Can anyone explain why the "rule of signs" leads to these two 
> results? We were surprised, for instance, that nothing was possible with a 
> method like Double Norwich.
>
> Despite this progress, course-splicing Helixoids were still not coming 
> forward. This led me to think about weaker splices, and the obvious line of 
> enquiry was the weakest/largest of all: if I added a further restriction, 
> that a row with (123) in a given arrangement in the Plain Bob must not only 
> have the same sign as its rotations, but must also match the sign of the same 
> row in the Helixoid plain course, then I could partition the extent into two 
> sets, with Plain Bob being rung from positive 123..... course ends, and the 
> Helixoid from negative 123..... course ends. Truth would be guaranteed under 
> these conditions.
>
> It turned out that millions of Helixoids matching the Plain Bob touch in this 
> way did exist, but unfortunately none of them appeared to satisfy Philip's 
> other requirements: to be Double, and to have one or more "splice-sister" 
> Helixoid methods which would go together in (for instance) a course-splice. 
> Just exhausting the list of Helixoids was very difficult, since for every 
> method I found in my initial searches there are maybe millions of trivial 
> variations, with either the back five or front three permuted amongst 
> themselves by alternative place notations.
>
> Expanding all these TVs and carrying out expensive checks for congruency with 
> the PB signs, plus searching for existence of splice sisters, looked 
> intractable. However in the end I found it was possible to construct a 
> processing pipeline which could tackle the job. First I searched the Helixoid 
> quarter-lead to identify all Double methods up to "Trivial Variation". (Of 
> course, I'd already done that bit). The second stage of the pipeline was to 
> expand TVs which generated different signs for the (123) arrangements. For 
> example, a method starting:
>
> 12345678
> 21436587 x
>
> Has different six TVs in that change, because there are six place notations 
> which keep the same pattern XX.X.... for the front and back five:
>
> 12345678
> 21435687 56
>
> 12345678
> 21435768 58
>
> 12345678
> 21435678 5678
>
> 12345678
> 12435687 1256
>
> 12345678
> 12435768 1258
>
> 12345678
> 12435678 125678
>
> But of these, only three affect the sign of the (123) row:
>
> -> place notations 56 and 58 both generate a negative row, hence different 
> from the cross change, but with 123 in the same position;
>
> -> place notation 125678 also generates a negative row, but here although 123 
> are in the same position, they have undergone a pair swap, meaning the sign 
> of the overall row needs to be the opposite of the original configuration.
>
> -> place notations 1256 and 1258 also have a pair-swap on (123), but generate 
> a positive not negative row.
>
> In practice I excluded more than two consecutive places, so 5678 and 125678 
> were not considered. This means that in general I limited the TV expansion to 
> at most three distinct types of place notation per change, whilst still 
> checking every possible type of Helixoid-to-PB row-sign match.
>
> Despite the pruning described above, stage 2 was the slowest part of the 
> pipeline, and the full search has only just completed.
>
> Once I had filtered down the expanded methods to that subset which was 
> "sign-congruent" with my PB touch, I ran stage 3 of the pipeline. Here the 
> remaining place notations were expanded (so 56 and 58 in the above example 
> would become distinct methods to consider), and looked for any method for 
> which a good set of splice-sisters existed. This immediately threw up the 
> outstanding examples of my "H and J" methods, which you can see in the 
> finished peal composition. Interestingly enough, nothing else particularly 
> worthy appeared even after exhaustive pipeline searches in smaller spaces, 
> and many days' running of the full pipeline.
>
> Now I have the full pipeline results I will investigate to see if this 
> conclusion is unaltered, and H and J really are the shining Helixoid 
> splice-sisters, or if other similar or even better examples exist.
>
> I hope that this explanation of my recent endeavours has been of interest, 
> and I'd be fascinated to hear if anyone can devise an explanation for the 
> "plain hunt" conundrum described above.
>
> Part of the fun of this particular composing exercise has been the 
> opportunity it has given me to play with a (relatively) new programming 
> language, Scala, and to discover how superbly well-suited it appears to be to 
> the task of computer composition. It was quite a revelation. I'll write a bit 
> about that in my next email.
>
> MBD
>
> _______________________________________________
> ringing-theory mailing list
> ringing-theory at bellringers.net
> http://bellringers.net/mailman/listinfo/ringing-theory_bellringers.net
>