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Re: Simplifying complicated expressions

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  • Subject: [mg110175] Re: Simplifying complicated expressions
  • From: "David Park" <djmpark at>
  • Date: Sun, 6 Jun 2010 06:41:49 -0400 (EDT)

"The normal 
/. and -> substitutions and patterns are not adequate for this."

That sounds like a completely unfounded statement so why don't you
demonstrate it?

David Park
djmpark at  

From: S. B. Gray [mailto:stevebg at ROADRUNNER.COM] 

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

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