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MathGroup Archive 2002

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Re: FullSimplify[Abs[Sign[x]],x>=0] equals 1?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg33731] Re: FullSimplify[Abs[Sign[x]],x>=0] equals 1?
  • From: "David W. Cantrell" <DWCantrell at sigmaxi.org>
  • Date: Wed, 10 Apr 2002 00:49:15 -0400 (EDT)
  • References: <a8tsnd$fkm$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Alain Cochard <al2 at noos.fr> wrote:
> Is the following behavior normal?
>
> In[1]:= Simplify[Abs[Sign[x]],x>=0]
>
> Out[1]= Abs[Sign[x]]
>
> In[2]:= FullSimplify[Abs[Sign[x]],x>=0]
>
> Out[2]= 1

Is this behavior similar to simplifying x/x to 1, even when x might be 0?
Maybe not. Anyway, you might be amused at the result of a typographical
error. (I had _intended_ to type logical OR, instead of logical AND.)

In[1]:= Simplify[Abs[Sign[x]], x>0 && x==0]

Out[1]= 1

Curious!

  David

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