Nice! (I feel like I should have seen that...)
Thanks, -- Raul On Sun, Oct 31, 2021 at 2:27 PM xash <xash@λ.land> wrote: > > With mixed bases, for e.g. 3: > 3 2 1 #: i. 6 > > An equivalent function of permh is thus: > (>:@i.@- #: i.@!) 3 > > If you want to map arbitrary n to a permutation with unknown length, > you could use something like this (I love J for things like !^:_1): > (#:~ [:>:@i.@-@<.@>: !^:_1)"0 (2+i.4) NB. needs special cases for 0/1 > > On Sun Oct 31, 2021 at 4:20 PM CET, Raul Miller wrote: > > (I really do not know the "right" historical terminology for talking > > about this, thus the subject line and the odd intro I am using here.) > > > > In the Tower of Hanoi puzzle, we move a stack of disks from one tower > > to another, moving only the top piece. > > > > But imagine that we could remove the disks in any order we choose, > > instead of only moving the top piece each time. And, imagine that > > instead of having three towers we had only two and that we cannot > > place disks back in the first tower. And, imagine that we have to put > > each disk down in the second tower in the order that we removed the > > disk from the first tower. > > > > In other words, this is a setup for generating arbitrary permutations. > > Except, indexing changes as we progress through the permutation. > > > > In other words, the indices of the removed disks for each permutation > > could be generated this way: > > > > permh=: (i.1 0)"_`([: ,/ i. ,"0 1/ $:@<:)@.* > > > > For example: > > > > permh 3 > > 0 0 0 > > 0 1 0 > > 1 0 0 > > 1 1 0 > > 2 0 0 > > 2 1 0 > > > > I am wondering if there's a concise way of expressing this using A. > > (or, some other expression which would eliminate the need to generate > > all such permutations when finding a specific permutation). > > > > Or, failing that, what terms would I search on to find previous work > > addressing this kind of thinking? > > > > Thanks, > > > > -- > > Raul > > ---------------------------------------------------------------------- > > For information about J forums see http://www.jsoftware.com/forums.htm > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
