       Setting order of variables other than alphabetical.

• To: mathgroup at smc.vnet.net
• Subject: [mg21077] Setting order of variables other than alphabetical.
• From: chesri <chesri at leonis.nus.edu.sg>
• Date: Sun, 12 Dec 1999 23:51:44 -0500 (EST)
• Organization: National University of Singapore
• Sender: owner-wri-mathgroup at wolfram.com

```Hello!

I am a regular user of MATHEMATICA, and while doing problems in
dynamical system theory, I have faced following problem.

Consider a term involving power series expansion terms. (These terms too
were generated using MATHEMATICA functions.)

( e x10 +d x01+ e^2 x20 + 2 ed x11 + d^2 x02 + ...) ( e x10 +d x01+ e^2
x20
+ 2 ed x11 + d^2 x02 + ...)

The term in third order should be, for x1 = x10 = x01,

e^3 (x1 x2 + x2 x1)

but MATHEMATICA re-orders terms in alphabetical order and writes the
term as

e^3 (2 x1 x2)

which is incorrect, if x1 and x2 are (column) vectors in R^n,
i.e. x1 x2 [\NOT] = x2 x1.

Now it is possible to define a variable as is done to define it to be a
real or integer by  setting an attribute, in MATHEMATICA as a general
condition, but it is not possible to define it as a vector.

Does anyone know how to effectively set this problem right?

Satish

```

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