MathGroup Archive 1997

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Curiosity about Sign[.] and Abs[.]

  • To: mathgroup at
  • Subject: [mg7258] Curiosity about Sign[.] and Abs[.]
  • From: Michael Hucka <hucka at>
  • Date: Tue, 20 May 1997 02:58:49 -0400 (EDT)
  • Organization: University of Michigan EECS, Ann Arbor, Mich., USA
  • Sender: owner-wri-mathgroup at

I'm sure this is simply due to my cluelessness about math in general, but can
someone explain to me in simple terms why the following occurs?

Suppose u and v are variables, both real.

In[72]:= foo = I u Sign[v]

Out[72]= I u Sign[v]

In[73]:= Abs[foo]

Out[73]= Abs[u]

What puzzles me is what happened to the value of the function foo at 0.
With the signum function in there, the value of foo at v = 0 should be 0
(because Sign[0] = 0), yet this seems to disappear after taking Abs[foo].

Mike Hucka    hucka at    University
 PhD to be, computational models of human visual processing (AI Lab)     of
   UNIX systems administrator & programmer/analyst (EECS DCO)         Michigan

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