Re: Question about the derivative of Abs
- To: mathgroup at smc.vnet.net
- Subject: [mg106174] Re: Question about the derivative of Abs
- From: David Bailey <dave at removedbailey.co.uk>
- Date: Mon, 4 Jan 2010 05:58:15 -0500 (EST)
- References: <hhkj64$53d$1@smc.vnet.net>
Sam Takoy 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
>
You could just clean up the answer by applying a suitable transformation:
expr /. {Abs'[y_]->1,Abs''[y_]->0}
David Bailey
http://www.dbaileyconsultancy.co.uk