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MathGroup Archive 2000

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Re: Bugs in Abs and Sign !?

  • To: mathgroup at
  • Subject: [mg25711] Re: Bugs in Abs and Sign !?
  • From: "Bill Bertram" <wkb at>
  • Date: Thu, 19 Oct 2000 04:35:35 -0400 (EDT)
  • Organization: Australian Nuclear Science and Technology Organisation
  • References: <8sjkr7$>
  • Sender: owner-wri-mathgroup at

Jack Goldberg <jackgold at> wrote in message
news:8sjkr7$g3p at
> Hi group.
> 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.

Hi Jack,

It does certainly looks like a bug, but in this case Mathematica seems to
have been smart enough to realise that ( at least for integer n),

   Sign[x^n] == Sign[x]^n, and ditto for Abs.

So fnt[x]^2 and fnt[x^2] are numerically identical.



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