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Curiosity about Sign[.] and Abs[.]

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

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 umich.edu    http://www.eecs.umich.edu/~hucka    University
 PhD to be, computational models of human visual processing (AI Lab)     of
   UNIX systems administrator & programmer/analyst (EECS DCO)         Michigan