That example wouldn't be a permutation in J, because J indices start at 0. But let's assume you meant to subtract 1 from each of those values...
Anyways, I think you are asking about this: https://www.jsoftware.com/help/dictionary/dccapdot.htm "If p is a permutation of the atoms of i.n, then p is said to be a permutation vector of order n, and if n=#b, then p{b is a permutation of the items of b ." So "a permutation" would a list of indices p such that (i.#p)-:/:~p And, an inverse permutation would be a list of indices ip such that (i.#p)-:ip{p So a function which produces the inverse of a permutation is /: And, a function composing two permutations into one is { Does this help? Thanks, -- Raul On Wed, Oct 16, 2019 at 12:53 PM <[email protected]> wrote: > > Hello again, > > To my understanding an example of the usual representation of a > permutation is 3 2 4 1, meaning the permutation takes 3 to 1, 2 to 2, > 4 to 3 and 1 to 4. The inverse is 4 2 1 3. OK? > > In J, > what is a function producing the inverse of a permutation? > what is a function composing two permutations into one? > > Thanks, ... Peter E. > > > > > > -- > https://en.wikibooks.org/wiki/Medical_Machines > Tel: +1 604 670 0140 Bcc: peter at easthope. ca > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
