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Re: Abs[x] function

• To: mathgroup at smc.vnet.net
• Subject: [mg87857] Re: Abs[x] function
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Fri, 18 Apr 2008 07:12:39 -0400 (EDT)
• Organization: Uni Leipzig
• References: <fu9fn7$c8d$1@smc.vnet.net>
• Reply-to: kuska at informatik.uni-leipzig.de

Hi,

because you have forgotten to define

Derivative[1][Abs][x_] := Sign[x]

Regards
   Jens

Vladislav wrote:
> Who can explain the behavior. THe derivative Abs[x] at x=.5 is well
> defined and is equal to 1.
> 
> In[1]:= D[Abs[x], x]
> 
> Out[1]=
> \!\(\*SuperscriptBox["Abs", "\[Prime]",
> MultilineFunction->None]\)[x]
> 
> In[2]:= % /. x -> .5
> 
> Out[2]=
> \!\(\*SuperscriptBox["Abs", "\[Prime]",
> MultilineFunction->None]\)[0.5]
>