Re: Newbie Question About An Error Message
- To: mathgroup at smc.vnet.net
- Subject: [mg55456] Re: [mg55443] Newbie Question About An Error Message
- From: Sseziwa Mukasa <mukasa at jeol.com>
- Date: Thu, 24 Mar 2005 03:41:55 -0500 (EST)
- References: <200503231034.FAA04057@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
On Mar 23, 2005, at 5:34 AM, Adam Hartshorne 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]
To make answering your question easier I'm going to interrupt here and
comment on this function. You have written a function abs which takes
one argument that should have at least three parts.
> Ok then I try
>
> D[(abs[{x-xi}])^2,x]
You have called your function abs with the argument {x-xi}, assuming x
and xi have not otherwise been defined this is a list with only one
part.
> 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.
I think these messages should make sense now.
> Any help will be much appreciated,
I hope this helped.
If you redefine your abs function as abs[x_]:=Sqrt[Plus@@#^2&/@x] then
you will no longer be making assumptions about the length of x and your
D[___] expression will work as you expected.
Regards,
Ssezi
- References:
- Newbie Question About An Error Message
- From: Adam Hartshorne <oracle3001@yahoo.com>
- Newbie Question About An Error Message