Re: trying to "simplify" very large output

• To: mathgroup at smc.vnet.net
• Subject: [mg83092] Re: trying to "simplify" very large output
• From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
• Date: Sat, 10 Nov 2007 03:43:48 -0500 (EST)
• Organization: The Open University, Milton Keynes, UK
• References: <fh1btf\$an7\$1@smc.vnet.net>

```Basjsmit wrote:

> When I used Mathematica to solve a certain expression, the output was
> extremely large, somewhere around 10 000 characters. When I looked more
> closely at the output, I noticed certain frases kept repeating. I havent
> found anything in the help, but Im wondering if there is a function that can
> replace those frases with a variable and set that variable once. An example:
>
> t-> -(y z-v x Cos[k]^2-v x Sin[k]^2)/(z^2-x^2 Cos[k]^2-x^2 Sin[k]^2)-1/2
> \[Sqrt]((4 (y z-v x Cos[k]^2-v x Sin[k]^2) ........
>
> becomes:
>
> A = y z-v x Cos[k]^2-v x Sin[k]^2
> B = z^2-x^2 Cos[k]^2-x^2 Sin[k]^2
> t-> -A / B -1/2 \[Sqrt]((4 A ........
>
>
> PS: just curious, is there a name for the proces I described above?

Transformation rules and replacement operators are your friends here.
You should familiarize yourself with the following set of tutorials,
available in the documentation center

tutorial/TransformationRulesAndDefinitionsOverview

or online at

http://reference.wolfram.com/mathematica/tutorial/TransformationRulesAndDefinitionsOverview.html

Regards,
--
Jean-Marc

```

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