Re: Question about the derivative of Abs

*To*: mathgroup at smc.vnet.net*Subject*: [mg106140] Re: [mg106097] Question about the derivative of Abs*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Sat, 2 Jan 2010 05:07:54 -0500 (EST)*Reply-to*: hanlonr at cox.net

sub = { Abs'[x_?NumericQ /; x != 0] -> Sign[x], Abs''[x_?NumericQ /; x != 0] -> 0}; Abs'[2.0] + Abs''[2.0] /. sub 1 Bob Hanlon ---- Sam Takoy <samtakoy at yahoo.com> wrote: ============= Hi, I kind of asked this question before, but in a more confusing context, so now I would like to ask it by itself. In the course of my computations, I get Abs' and Abs''. It is applied to a positive number, so I think those values should be 1 and 0. However, Mathematica fails to simplify it. For example In[34]:= Abs'[2.0] Out[34]= \!\(\*SuperscriptBox["Abs", "\[Prime]", MultilineFunction->None]\)[2.] These expressions really mess up my answers. How do I get Mathematica to do these simplifications? Thanks Sam