       linear equations with indexed variables?

• To: mathgroup at smc.vnet.net
• Subject: [mg6896] linear equations with indexed variables?
• From: hxie at gradin.cis.upenn.edu (Hong-liang Xie)
• Date: Fri, 25 Apr 1997 14:00:30 -0400 (EDT)
• Organization: University of Pennsylvania
• Sender: owner-wri-mathgroup at wolfram.com

```I am new to Mathematica and I need to solve a system of
linear equations whose variables are indexed (i.e., x,
x, x), for example,

3x[i] = 2x[i+1] + x[i-1] ( 1 <= i <= 3)
x[4 ]  = 1
x   = 0

The above is a system of 5 linear equations with
5 variables x, x, x, x, x.  I can certainly
rewrite it into 5 equations using 5 variables x0, x1, x2,
x3, x4.  However, if the range of i gets bigger, or, worse,
if each x has two indexes as in x[i,j], this rewriting could
get of hand quickly.  I tried different equation solving
functions in Mathematica but with no luck.  I would therefore
appreciate help from experts here on how to solve this kind of
equations directly.  Thanks a lot!

Hong
CIS Dept
Univ of Pennsylvania

```

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