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MathGroup Archive 2000

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Re: Simplify[] shortcoming

  • To: mathgroup at smc.vnet.net
  • Subject: [mg21570] Re: [mg21525] Simplify[] shortcoming
  • From: BobHanlon at aol.com
  • Date: Sat, 15 Jan 2000 02:04:12 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

expr = (3*x + (x - y)*Log[x] + (x - y)*Log[-1 + y/x])/(x - y);

expr // Apart // Simplify

(3*x)/(x - y) + Log[x] + Log[y/x - 1]

Bob Hanlon

In a message dated 1/14/2000 4:04:26 AM, gorni at dimi.uniud.it writes:

>I have run into a simple expression for which both Simplify and
>FullSimplify cannot see an easy simplification:
>
>expr = (3*x + (x - y)*Log[x] + (x - y)*Log[-1 + y/x])/(x - y);
>
>You can see that the factors (x-y) cancel out with the denominator.
>So you can write expr as
>
>(3*x)/(x - y) + Log[x] + Log[-1 + y/x]
>
>which has a LeafCount of 21, while expr scored 34. Nevertheless,
>Simplify[] leaves expr as it was.
>
>FullSimplify[expr] does collect (x-y) in the numerator, but still
>the LeafCount is 29.
>
>My version is Mathematica 4 on MacOS.
>


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