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MathGroup Archive 2003

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Re: Derivative help

  • To: mathgroup at smc.vnet.net
  • Subject: [mg39468] Re: Derivative help
  • From: Paul Abbott <paul at physics.uwa.edu.au>
  • Date: Mon, 17 Feb 2003 04:34:51 -0500 (EST)
  • Organization: The University of Western Australia
  • References: <b1dg35$7ar$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

In article <b1dg35$7ar$1 at smc.vnet.net>,
 "Steve Chiang" <stevezx at attbi.com> wrote:

> Hi, all.  I'm new to Mathematica.  I went to the help section for my
> question but it only further confused me.  I'm basically trying to take the
> first derivative of (ln(x))^x.  Here is my syntax: f = (ln(x))^x. 

In contrast to most responses in this thread this syntax is ok -- as 
long as you use TraditionalForm for input (under the Cell menu | Default 
Input FormatType). Personally I prefer TraditionalForm for input and 
output.

> But then when I evaluate f ', it says nothing but ((ln(x))^x)' which is 
> nothing new.

In TraditionalForm you could enter

   f = (ln(x))^x
   D[f,x]

Alternatively, you can make f an explicit function of x, 

   Clear[f]
   f[x_] = (ln(x))^x
   f'[x]

or make f a pure function.

   Clear[f]
   f = Function[x, (ln(x))^x]
   f'

Cheers,
Paul



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