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Re: Abs and Sign anomolies

• To: mathgroup at smc.vnet.net
• Subject: [mg7411] Re: Abs and Sign anomolies
• From: hans.steffani at e-technik.tu-chemnitz.de (Hans Steffani)
• Date: Sat, 31 May 1997 15:07:19 -0400 (EDT)
• Organization: University of Technology Chemnitz, FRG
• Sender: owner-wri-mathgroup at wolfram.com

Jack Goldberg <jackgold at math.lsa.umich.edu> writes:


>In[1]	Abs[Sign[x]] 
>Out[1]  1

My system delivers:
In[1] Abs[Sign[x]] // Simplify
Out[1] Abs[Sign[x]]

and

In[2] Abs[Sign[0]]
Out[2] 1

h.f.s.


>which is wrong if  x = 0.  For, Sign[0] = 0 and Abs[0] = 0.  So that the
>output of  Abs[Sign[x]] should be unsimplified. Indeed, Mma returns

>	Abs[Sign[0]] = 0

>Although multiple crashes (hard and soft) and exporting graphics are
>extremely annoying, a mathematical "bug" is a far more serious problem.
>A programming error like this can lead to disaster and I urge the
>newsgroup to post all such anomalies as soon as they are discovered. We
>cannot assume that contacting Wolfram Research will result in a warning
>in their FAQ site, nor a timely fix.  

>Wouldn't it be nice if someone (other than Wolfram Research)) could keep
>track of all mathematical "bugs" much the way one of our people keep
>track of relative speeds of the kernel on different platforms?  The
>advantages for all of us are so clear that no argument need be given.

>I would be willing to do this, but - I'm embarrasses to admit - I don't
>know how to set up a Web page or whatever so that people could access
>the complilations automatically!  If anyone wishes to send me their
>discoveries I will be happy to confirm them and keep a list. 

>Jack Goldberg
>University of Michigan 
>Ann Arbor Michigan
>e-mail:  jackgold at math.lsa.umich.edu

--
Hans Friedrich Steffani
Institut fuer Elektrische Maschinen und Antriebe, TU Chemnitz-Zwickau
mailto:hans.steffani at e-technik.tu-chemnitz.de
http://www.tu-chemnitz.de/~hfst/