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

[Alexander Holroyd]

Never mind, I see Philip sent it.

On Mon, 2 Jul 2012, Alexander Holroyd wrote:

> 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
>> 
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>
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