Re: Newbie Question About An Error Message

• To: mathgroup at smc.vnet.net
• Subject: [mg55457] Re: [mg55443] Newbie Question About An Error Message
• From: DrBob <drbob at bigfoot.com>
• Date: Thu, 24 Mar 2005 03:41:56 -0500 (EST)
• References: <200503231034.FAA04057@smc.vnet.net>
• Reply-to: drbob at bigfoot.com
• Sender: owner-wri-mathgroup at wolfram.com

```This is a correct answer for the given input:

D[abs[{x - xi}]^2, x]

2*abs[{x - xi}]*
Derivative[{1}][abs][{x - xi}]

But you meant Abs, not "abs", and make sure x doesn't have a value, or you'll get an error differentiating with respect to a constant.

The other error (from Part) can't come from that input, so I think you haven't sent us the input as it actually was.

Bobby

On Wed, 23 Mar 2005 05:34:54 -0500 (EST), Adam Hartshorne <oracle3001 at yahoo.com> wrote:

> Hi All,
>
> I am a real newbie to mathematica and have just encountered the
> following error message and I have no idea why and what it means.
>
> I have written a function to calculate the abs of a vector as follows
>
> abs[x_] := Sqrt[x[[1]]^2+x[[2]]^2+x[[3]]^2]
>
> then i was doing the following fine until a few moments ago and
> mathematica starting complaining. I am to my knowledge not asking
> anything different to what I asked it before, but I don't know enough
> about mathematica to know much more.
>
> Ok then I try
>
> D[(abs[{x-xi}])^2,x]
>
> Which is know the answer to is 2(x-xi), and mathematica has given me the
> answer. However now it is saying, maybe I have changed my input and no
> am typing something wrong.
>
> Part::partw: Part 2 of {x - xi} does not exist.
>
> Part::partw: Part 3 of {x - xi} does not exist.
>
> Any help will be much appreciated,
>
>
>
>
>

--
DrBob at bigfoot.com

```

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