My thinking is expression in the transformations of the original list of items, [0,1,2,3]. If you first transpose the 2nd and third position you get [0,1,3,2] and then if you transpose 1st and 2nd position you get [0,3,1,2]. You'll see my name all over the docs for that module so if you can find the error in my thinking here, you are close to the source ;-)
/c On Thursday, March 11, 2021 at 9:47:05 PM UTC-6 [email protected] wrote: > Hi Chris, > > Thanks for your response. When you write, > > > If you let `p = Permutation(1,2)(2,3)` then `p.list()` gives `[0, 3, 1, > 2]` which is consistent with R to L interpretation > > I think this is incorrect (and I contend that the docs are incorrect on > this point as well). > Multiplying the transpositions (1,2)(2,3) from R to L, we end up with the > cycle (1,2,3), > which in list form is [0, 2, 3, 1] (if `p.list()` is the second line of > 2-line permutation notation). > > What do you think? > > On Thu, Mar 11, 2021 at 7:33 PM Chris Smith <[email protected]> wrote: > >> So documentation here, "The composite of two permutations p*q means first >> apply p, then q" should read "...apply q, then p", right? This would be an >> easy issue to open and fix if there is consensus that it is wrong as >> written. But note that using the composition of function syntax reverses >> the order, "One can use also the notation p(i) = i^p, but then the >> composition rule is (p*q)(i) = q(p(i)), not p(q(i)):" >> >> /c >> >> On Thursday, March 11, 2021 at 8:37:25 PM UTC-6 Chris Smith wrote: >> >>> Given elements `0,1,2,3`, `Permutation(1,2)(2,3)` interpreting R to L >>> gives `0123->0132->0312`; interpreting L to R gives `0123->0213->0231` >>> >>> If you let `p = Permutation(1,2)(2,3)` then `p.list()` gives `[0, 3, 1, >>> 2]` which is consistent with R to L interpretation. So the assumption that >>> spelling it `Permutation(1,2)*Permutation(2,3)` means left to right must be >>> wrong? >>> >>> /c >>> >>> On Monday, February 22, 2021 at 3:51:02 PM UTC-6 [email protected] wrote: >>> >>>> Hi everyone, >>>> >>>> I've been experimenting with the "Permutations" module, trying to >>>> follow the examples in the documentation here: >>>> >>>> https://docs.sympy.org/latest/modules/combinatorics/permutations.html >>>> >>>> As expected, >>>> >>>> Permutation(1, 2)(2, 3) == Permutation(1, 2) * Permutation(2, 3) >>>> >>>> But doesn't this mean that the permutations are applied from left to >>>> right, since (as described in the docs) left-to-right permutation >>>> multiplication p*q is equivalent to composition q o p? >>>> >>>> If so, this contradicts the documentation's claim that "The convention >>>> is that the permutations are applied from *right to left*". >>>> >>>> If not, I must be confused about something, and would appreciate any >>>> corrections. >>>> >>>> Thanks for your help, >>>> Alex >>>> >>>> -- >> You received this message because you are subscribed to a topic in the >> Google Groups "sympy" group. >> To unsubscribe from this topic, visit >> https://groups.google.com/d/topic/sympy/5MTQFwB7xIo/unsubscribe. >> To unsubscribe from this group and all its topics, send an email to >> [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/sympy/7556df78-eb14-408c-bf38-326dafaa1318n%40googlegroups.com >> >> <https://groups.google.com/d/msgid/sympy/7556df78-eb14-408c-bf38-326dafaa1318n%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/b0302a20-7afa-48e7-ac63-2f467c0b164cn%40googlegroups.com.
