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MathGroup Archive 2004

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Re: Abs function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg47281] Re: Abs function
  • From: bobhanlon at aol.com (Bob Hanlon)
  • Date: Fri, 2 Apr 2004 03:30:28 -0500 (EST)
  • References: <c4ge4p$5a$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

It means that it does not know the derivative of Abs.  You need to express Abs
in terms of a function for which it knows the derivative.

D[x(2UnitStep[x]-1), x]

2*x*DiracDelta[x] + 2*UnitStep[x] - 1

Simplify[%, #]& /@ {x<0, x>=0}

{-1, 1}

D[If[x<0, -x, x], x]

If[x < 0, -1, 1]


Bob Hanlon

In article <c4ge4p$5a$1 at smc.vnet.net>, nikmatz <nikmatz at math.ntua.gr> wrote:

<< i try to find the derivative of abs function

D[Abs[x],x]

and Mathematica answer
Abs`[x]

what mean that


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