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

  • To: mathgroup at
  • Subject: [mg33691] FullSimplify[Abs[Sign[x]],x>=0] equals 1?
  • From: Alain Cochard <al2 at>
  • Date: Tue, 9 Apr 2002 01:01:51 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

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

In[3]:= $Version

Out[3]= 4.1 for Sun Solaris (November 8, 2000)

In this case I would have expected FullSimplify to give the save
answer as Simplify, as I was (naively?) assuming Abs[Sign[0]] equals
zero.  What am I missing?  (Note I get the same output 
for Version 4.0 for Linux (July 22, 1999).)


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