       Re: Odd ordering of results?

• To: mathgroup at smc.vnet.net
• Subject: [mg99598] Re: [mg99527] Odd ordering of results?
• From: peter <plindsay.0 at gmail.com>
• Date: Fri, 8 May 2009 00:20:56 -0400 (EDT)
• References: <200905071035.GAA19398@smc.vnet.net>

```is this a "set" versus "list" issue perhaps; i.e. list is ordered, set isn't ?
Peter

2009/5/7 AES <siegman at stanford.edu>:
> I'm evaluating an optical interferometer problem in which an input wave
> e1 produces internal, reflected and transmitted waves e2 thru e7 that
> are connected by the linear equations
>
>   waveEqns = {e1 == 1, e2 == rho12 e1 + t42 e4, e3 == rho=
43 e4 + t13 e1,
>       e4 == gL e6, e5 == gL e3, e6 == rho56 e5, e7 ==
= t57 e5};
>
> where the rho_nm and t_nm are reflection and transmission coefficients
> and the input wave amplitude is arbitrarily set to e1==1; and then
> solving these using
>
>  waveSolns = Solve[waveEqns, {e2, e3, e4, e5, e6, e7}]
>
> and getting a set of rules en-><stuff> for e2 thru e7 which are ordered
> in the sequence
>
>   Out[] = {{e2  e7  e3  e6  e5  e4 }}
>
> with the "stuff" stripped out for brevity.
>
> What puzzles me -- not a problem, just curious -- is the _order_ in
> which these rules appear.
>
> Even more puzzling:  If I take out the leading "e1==1," statement i=
n
> waveEqns I get the same results, except each "stuff" becomes
> "e1*same_stuff" -- and the set of rules produced by waveSolns is now in
> the different order
>
>   Out[] = {{e2  e7  e3  e4  e5  e6 }}
>
> Odd . . .  (seems like the natural thing would be to order the list on
> the left side of the en-><stuff> terms, getting e2 to e7 in either case)
>
>

--
Peter Lindsay

```

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