Re: Wierdness with the laplacian
- To: mathgroup at smc.vnet.net
- Subject: [mg45153] Re: Wierdness with the laplacian
- From: "Peltio" <peltio at twilight.zone>
- Date: Thu, 18 Dec 2003 06:55:29 -0500 (EST)
- References: <brpm16$7u4$1@smc.vnet.net>
- Reply-to: "Peltio" <peltioNOSP at Miname.com.invalid>
- Sender: owner-wri-mathgroup at wolfram.com
"Peter Jay Salzman" wrote
> <<Calculus`VectorAnalysis`
> SetCoordinates[Spherical[r, theta, phi]
> Laplacian[ Exp[r^2] ]
>
>Mathematica gives:
>
> 2 2
> r 2 r 4
>Csc[theta] (6 E r Sin[theta] + 4 E r Sin[theta])
>------------------------------------------------------
> 2
> r
>
>Which is wrong since Exp[r^2] is not a function of theta or phi.
Nor is the function returned by Mathematica. : )
Csc is the cosecant, or the reciprocal of the Sin function.
It makes the expression repent and deny its dependence on theta.
Csc[x]*Sin[x] == 1
An Expand or a Simplify are the cure for your Laplacian's illness.
cheers,
Peltio
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