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MathGroup Archive 2005

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Newbie Question About An Error Message

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55443] Newbie Question About An Error Message
  • From: Adam Hartshorne <oracle3001 at yahoo.com>
  • Date: Wed, 23 Mar 2005 05:34:54 -0500 (EST)
  • Organization: University of Warwick, UK
  • Sender: owner-wri-mathgroup at wolfram.com

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,

Adam


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