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Re: Subscripted variables and function definitions
 To: mathgroup at smc.vnet.net
 Subject: [mg65203] Re: Subscripted variables and function definitions
 From: "JensPeer Kuska" <kuska at informatik.unileipzig.de>
 Date: Fri, 17 Mar 2006 05:45:43 0500 (EST)
 Organization: Uni Leipzig
 References: <dvdida$a26$1@smc.vnet.net>
 Sender: ownerwrimathgroup at wolfram.com
Hi,
you should use Symbolize[] from the Notation package, if
you need Subscript[_,_] in a function pattern.
and X[1] is a *function* call to the function X[]
with the arguments 1 while
X[[1]] is the Part[], i.e., the first element of
the value of X, and the value of X should be a list.
You mix up both and that cause your problems.
Regards
Jens
"Geico Caveman" <spam at spam.invalid> schrieb im
Newsbeitrag news:dvdida$a26$1 at smc.vnet.net...
 Hi

 I am trying to define a function (using the
front end  I will be using
 latex syntax in this post to make clear what I
am doing) :

 A[k_s_,r_t_,r_k_]:=...

 Now after this, if I try to output A[1,1,1], it
just throws A[1,1,1] back.
 However, if I define :

 A[ks_,rt_,rk_]:=...

 it gives the right answer. Two questions :

 1. Why aren't subscripted variable names treated
the same as other variable
 names in this context ?

 2. Is there a way to coax Mathematica into doing
what I am trying to do
 above ?

 Mathematica is a nice system, but it has these
highly irritating quirks.


 Another (unrelated) question :

 I have a 4x4 matrix which is a function of some
variables :

 A:=... (function of r1,r2,r3, ...)

 f:=... (function of the same variables)

 X:=Inverse[A] . f

 Now, I want to extract a ratio :

 X[1]/(X[3]+X[4]) and assign it to a function :

 g[r1_,r2_,r3_]:=X[1]/(X[3]+X[4])

 A test evaluation of g[1,1,1] throws g[1,1,1]
back. Makes no sense at all to
 me. What am I missing, and why is Mathematica so
unintuitive here ?

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