[r-t] Big searches

Graham John graham at changeringing.co.uk
Thu Dec 27 12:00:42 UTC 2007

Mike wrote:

> Out of curiosity I subsequently ran a search for 720s 
> (of MUG Minor) with bob=14, single=1456, at the section
> end.  It took several months to complete, but sadly I
> have no idea how many nodes.

It would depend on the pruning algorithm and optimisation you used. I wrote
an assembler program to do this (in 1989!) to take advantage of the the fact
that each division contains all the possible rows with an arrangement of
three pairs of bells, resulting in an economic bit proving table. The most
important optimisation is to avoid the massive repetition of effort caused
by singles, by removing the following equivalences.

--- -ss s-s ss-
sss s-- -s- --s
-s s-
-- ss

This is easy to do by only generating a single following a plain lead, never
after a bobbed or singled lead.

I didn't count the nodes either! 


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