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MathGroup Archive 2005

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Unexpected behavior of Simplify

  • To: mathgroup at smc.vnet.net
  • Subject: [mg63229] Unexpected behavior of Simplify
  • From: gleam at flashmail.com
  • Date: Tue, 20 Dec 2005 04:19:26 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Hello MathGroup.

What is the explanation for this behavior?

In[1]:=
\!\(ClearAll[a, b, c]\[IndentingNewLine]
   \(expr = c\^4\ b\^2 + a\^4\ b\^2 + c\^2\ a\^2\ \((1 - 2\ b\^2)\);\)\
\[IndentingNewLine]
   Simplify[expr]\[IndentingNewLine]
   Simplify[expr /. {a -> b, b -> a}] /. {a -> b, b -> a}\)
Out[3]=
\!\(a\^4\ b\^2 + a\^2\ \((1 - 2\ b\^2)\)\ c\^2 + b\^2\ c\^4\)
Out[4]=
\!\(a\^2\ c\^2 + b\^2\ \((a\^2 - c\^2)\)\^2\)

The second application of the replacement is merely for clarity; the 
unexpected behavior is present without it.

Paul


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