Re: Re: Newbie Question About An Error Message

*To*: mathgroup at smc.vnet.net*Subject*: [mg55476] Re: [mg55463] Re: [mg55443] Newbie Question About An Error Message*From*: Mitch.Stonehocker at sungard.com*Date*: Fri, 25 Mar 2005 05:48:17 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Hi, Your function abs[x1_, x2_, x3_] specifies three arguments. With D[(abs[{x-xi}])^2,x] you only give it one argument. If you include the two remaining arguments D[(abs[{x - xi}, x2, x3])^2, x] you get 2 (x - xi) Cheers, Mitch Stonehocker -----Original Message----- From: Matthias Bode [mailto:lvsaba at hotmail.com] To: mathgroup at smc.vnet.net Subject: [mg55476] [mg55463] Re: [mg55443] Newbie Question About An Error Message Hello Adam: 1. INPUT: abs[x1_, x2_, x3_] := Sqrt[x1^2 + x2^2 + x3^2] INPUT: abs[1, 2, 3] OUTPUT: Sqrt[14] 2. D[(abs[{x-xi}])^2,x] does NOT give the answer you know but: INPUT: D[abs[{x - xi}]^2, x] yields: OUTPUT: 2*abs[{x - xi}]*Derivative[{1}][abs][{x - xi}] whereas INPUT: D[Abs[(x - xi)^2], x] yields: OUTPUT: 2*Abs[x - xi]*Derivative[1][Abs][x - xi], with [Abs] absolutely unequal to [abs]! Finally D[(x - xi)^2, x] gives: 2*(x - xi), the answer you know. MATHEMATICA which I have been using since version 2 does work really fine if the user deigns to heed its syntax rules; insofar it is VERY similar to ALL other programming languages. Best regards, MATTHIAS BODE Torres Sofer III, depto. 9 A Pedro Borda #1072 esq. Ismael Vasquez COCHABAMBA/BOLIVIA CEL: +591-70 71 56 64 TEL/FAX: +591-4-4 53 34 17 LVSABA at HOTMAIL.COM Time indicated: UTC (=GMT). ----- Original Message ----- From: "Adam Hartshorne" <oracle3001 at yahoo.com> To: mathgroup at smc.vnet.net Subject: [mg55476] [mg55463] [mg55443] Newbie Question About An Error Message > 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 > >