There is only one cycle, yes. The point of the example was to demonstrate
pathology with a very long cycle.
On Fri, 17 Mar 2023, Jan-Pieter Jacobs wrote:
Probably it's just something going over my head, but how do these
permutations have more than one cycle?
#@C. _1 1 |."0 _ i. 128
1 1
C.
Oh, nice! I tried <./{~^:(<2>.@^.#p)p, but that loses information; your
solution retains it in m.
On Thu, 16 Mar 2023, Marshall Lochbaum wrote:
Interesting problem! I think this works: for starting permutation p,
keep two lists. At step i,
- l is {~^:i p, that is, the index 2^i steps further
Probably it's just something going over my head, but how do these
permutations have more than one cycle?
#@C. _1 1 |."0 _ i. 128
1 1
C. y returns boxed cycles in permutation y.
What am I missing?
Jan-Pieter
On Fri, 17 Mar 2023, 01:07 Marshall Lochbaum, wrote:
> Interesting problem! I thin
J phrases is good source too.
https://www.jsoftware.com/docs/help807/phrases/rank_class.htm
On Fri, 17 Mar 2023 at 12:35 AM Devon McCormick wrote:
> This is good to know - thanks!
>
> On Wed, Mar 15, 2023 at 8:40 PM Ric Sherlock wrote:
>
> > As an adverb we can get the ascending and descendin
Interesting problem! I think this works: for starting permutation p,
keep two lists. At step i,
- l is {~^:i p, that is, the index 2^i steps further along the cycle
- m is the minimum index among those less than 2^i steps ahead.
Initially l is p and m is i.#p . To update, simultaneously replace l
I don't think so. If you wished to, you might rouse some interest by posting
some solutions yourself.
On Sun, 12 Mar 2023, Tony Poole wrote:
I see that Dyalog sponsors an annual APL Problem Solving Competition. Are
J solutions to these problems posted anywhere?
--
I can characterise the cycles of a permutation with (<.{~)^:_ (this keys each
cycle by its lowest element, but any unique key is fine).
But although this sometimes has log span (in the length of the longest cycle):
# (<.{~)^:(<_) _1|.i.128
8
The worst case is linear span:
# (<.{~)^:(<_)
This is good to know - thanks!
On Wed, Mar 15, 2023 at 8:40 PM Ric Sherlock wrote:
> As an adverb we can get the ascending and descending by applying either /:
> or \:
>
> open 'stats/base/univariate' NB. in JQt will open the script
>
> rankCompete=: 1 :'u~ i. ]'
>
> On Thu, Mar 16, 2023 at 1:30
