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