[Date Index] [Thread Index] [Author Index]

Re: Simplifying complicated expressions

• To: mathgroup at smc.vnet.net
• Subject: [mg110452] Re: Simplifying complicated expressions
• From: Harrie Kraai <hakraai at xs4all.nl>
• Date: Sat, 19 Jun 2010 07:47:08 -0400 (EDT)
• References: <hudci1$d68$1@smc.vnet.net>

I asked a similar question about a year ago,
http://groups.google.com/group/comp.soft-sys.math.mathematica/msg/a95d4651a5634771

and got this as the best answer:
http://groups.google.com/group/comp.soft-sys.math.mathematica/msg/7cca617e1b4928c6

leading me to Experimental`OptimizeExpression

But, also look at
http://www.wolfram.com/technology/guide/CommonSubexpressionDetectionCollection/
perhaps Mathematica is doing something behind the scenes already.

Harrie

S. B. Gray wrote:
> Suppose I  have a long complex expression in which terms like
> (x^2+y^3-x^2y^2+Sqrt[z3+y2]) (for a simple example) appear many times 
> along with various powers and the reciprocals of it, etc. To make the 
> expression comprehensible and to make the computation faster, I would 
> like to substitute say "f1xyz" for it everywhere it appears. The normal 
> /. and -> substitutions and patterns are not adequate for this. Of 
> course at evaluation time I want to compute f1xyz only once and not have 
> the final formula revert to the original variables. How do I prevent that?
> 
> Also a welcome addition to Mathematica would be the ability to find these 
> repeated expressions automatically and put them in, because doing it 
> manually is very error-prone and slow.
> 
> Tips will be appreciated!
> 
> Steve Gray
> 
>