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Re: Multiplying permutations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg41751] Re: Multiplying permutations
  • From: "Carl K. Woll" <carlw at u.washington.edu>
  • Date: Wed, 4 Jun 2003 08:34:36 -0400 (EDT)
  • Organization: University of Washington
  • References: <bbhvu4$75u$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Wolfgang,

Here is one possibility:

p_\[CenterDot]q_ :=Range[Length[p]][[Ordering[p]]][[Ordering[q]]]

where I use \[CenterDot] (which has the alias esc . esc) for the product.

For your example,

In[16]:=
p={3,1,2};
q={2,1,3};
p\[CenterDot]q
Out[18]=
{3, 2, 1}

as you requested.

Carl Woll
Physics Dept
U of Washingont

"Dr. Wolfgang Hintze" <weh at snafu.de> wrote in message
news:bbhvu4$75u$1 at smc.vnet.net...
> Is there a simple command in Mathematica to multiply two permutations,
> i.e. to carry out one after the other?
>
> I looked at the packages DiscreteMath`Permutations` and
> DiscreteMath`Combinatorica` but couldn't find it.
>
> Example
>
> p = {3,1,2}  mapping: 1->3, 2->1, 3->2
> q = {2,1,3}  mapping: 1->2, 2->1, 3->3
> p.q = mappings (p first, then q)
> [1-p->3-q->3, 2-p->1-q->2, 3-p->2-q->1]
> = {3,2,1}
>
> Any help appreciated
>
> Wolfgang
>



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