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MathGroup Archive 2000

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Re: Bugs in Abs and Sign !?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg25717] Re: [mg25674] Bugs in Abs and Sign !?
  • From: BobHanlon at aol.com
  • Date: Thu, 19 Oct 2000 04:35:40 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

In a message dated 10/18/2000 3:42:54 AM, jackgold at umich.edu writes:

>Try,
>
>Abs[x^2] /. Abs[u_] -> fnt[u] 
>
>and 
>
>Sign[x^2] /. Sign[u_] -> fnt[u]
>
>In each case I get  fnt[x]^2.  Shouldn't I get  fnt[x^2]? After all,
>g[x^2] /. g[u_] -> fnt[u]  returns fnt[x^2] which is what I have been led
>to expect from Mathematica.  I am using ver 4.01 on a PowerMac.
>
>These peculiarities are driving me crazy.  This is the fourth "bug" I have
>found in just 2 weeks.  Please tell me I'm wrong.

The functions are evaluated before the substitution

{Abs[x^2] , Sign[x^2]}

{Abs[x]^2, Sign[x]^2}

Release[Hold[Abs[x^2] ] /. Abs[u_] -> fnt[u] ]

fnt[x^2]


Bob Hanlon


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