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Re: Curl and Div problems

  • To: mathgroup at smc.vnet.net
  • Subject: [mg115535] Re: Curl and Div problems
  • From: Peter Breitfeld <phbrf at t-online.de>
  • Date: Thu, 13 Jan 2011 03:30:59 -0500 (EST)
  • References: <igjr0p$928$1@smc.vnet.net>

sean k wrote:

> I'm having problems with VectorAnalysis package.
>
> Within the documentation center, the package loads and works fine.
>
> But in a notebook, it seems to highlight Curl in red and neither Div
> or Curl works properly.
>
> Needs["VectorAnalysis`"]
>
> {D[x^2 y, x] + D[ x z, y] + D[ x^2 y^3, z]}
>
> Div[{x^2 y, x z, x^2 y^3}]
>
> gives different answers.
>
> {2 x y}
> 0
>
>
> Curl[{x^2 y, x z, x^2 y^3}]
>
> gives
>
> {0,0,0}
>
>
> I'm on windows vista home edition, 64 bit, Mathematica 8.0.
>
> Does anyone else have this problem?
>
>

I think you missed to define the coordinate-variables:

Needs["VectorAnalysis`"]
In:= Coordinates[]
Out= {Xx,Yy,Zz}

These are the default coordinates Mathematica uses after loading the
package. You will change them to

In:= SetCoordinates[Cartesian[x,y,z]]
Out= Cartesian[x,y,z]

In:= Coordinates[]
Out= {x,y,z}

Now it works:

field={x^2 y,x z,x^2 y^3};

In:= Div[field]
Out= 2x y

In:= Curl[field]
Out= {-x+3x^2 y^3,-2x y^3,-x^2+z}

Curl shows up in red on my machine too, but works as it should. Seems to
be a little bug, introduced in v.8

-- 
_________________________________________________________________
Peter Breitfeld, Bad Saulgau, Germany -- http://www.pBreitfeld.de


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