       Re: Re: derivative of a well-behaved function

• To: mathgroup at smc.vnet.net
• Subject: [mg99728] Re: [mg99631] Re: derivative of a well-behaved function
• From: Syd Geraghty <sydgeraghty at me.com>
• Date: Tue, 12 May 2009 03:10:17 -0400 (EDT)
• References: <gtrl0i\$1mf\$1@smc.vnet.net> <200905100912.FAA09609@smc.vnet.net>

Hi Maxim,

I get the following error message evaluating your expression with my
system setup as listed below:

> D[f[g[z]], z, Direction -> z0] ==
>  g'[z]*D[f[w], w, Direction -> z0*g'[z]] /. w -> g[z]

and Direction is highlighted in red.

D::optx: Unknown option Direction in D[f[g[z]],z,Direction->z0]. >>

D::optx: Unknown option Direction in D[f[w],w,Direction->z0 (g^\
[Prime])[z]]. >>

D::optx: Unknown option Direction in D[f[g[z]],g[z],Direction->z0 (g^\
[Prime])[z]]. >>

General::stop: Further output of D::optx will be suppressed during
this calculation. >>

In my documentation Direction is listed as an option for Limit[]

Are you running a developer version?

Syd Geraghty B.Sc, M.Sc.

sydgeraghty at mac.com

Mathematica 7.0.1 for Mac OS X x86 (64 - bit) (18th February 2009)
MacOS X V 10.5.6
MacBook Pro 2.33 GHz Intel Core 2 Duo  2GB RAM

On May 10, 2009, at 2:12 AM, m.r at inbox.ru wrote:

> Essentially you want to compute a directional derivative of f[g[z]]
> with g analytic and f non-analytic, where f == Abs and the direction
> vector z0 == 1. Then (making up the notation as we go along)
>
> D[f[g[z]], z, Direction -> z0] ==
>  g'[z]*D[f[w], w, Direction -> z0*g'[z]] /. w -> g[z]

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