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MathGroup Archive 2006

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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: "Jens-Peer Kuska" <kuska at informatik.uni-leipzig.de>
  • Date: Fri, 17 Mar 2006 05:45:43 -0500 (EST)
  • Organization: Uni Leipzig
  • References: <dvdida$a26$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup 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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