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/CABL__EuuvFk01ZmSYZNkvNTpYtktHbWEM8_s5%2B%3D8B0JmBV8%2Bcg%40mail.gmail.com.
