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MathGroup Archive 2004

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Re: Question: ABS and \[Prime]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg47484] Re: Question: ABS and \[Prime]
  • From: "David W. Cantrell" <DWCantrell at sigmaxi.org>
  • Date: Wed, 14 Apr 2004 07:16:32 -0400 (EDT)
  • References: <c5gfrm$apq$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

wellsed at wam.umd.edu (Ed Wells) wrote:
> In my notebook output, a copy of which can be seen at :
>
> www.glue.umd.edu/~wellsed/derivatives.html
>
> I'm finding the derivatives of a complex function involving distances
> (R[] is a distance function) in an energy function (W[] is an energy
> function).

Having looked at your notebook, I must guess that, when you said "complex"
above, you simply meant "complicated". Perhaps Abs was used merely to avoid
getting a negative number under Sqrt. If that is the case, then look at the
thread "Abs function", started earlier this month by nikmatz, at
<http://groups.google.com/groups?threadm=c4j9sq%24dha%241%40smc.vnet.net>.

> Each of my derivatives looks okay except for the presence
> of the Abs[] function with a \[Prime] following it.  It does not
> appear in every instance, but I cannot find any documentation for what
> this may mean.  An example is in the first line of Out[36].

As explained in the cited thread, the prime mark means "derivative". That
thread also gives ways to avoid getting Abs', assuming that your quantities
are real numbers.

HTH,
David


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