Re: wrong divergence?!?

• To: mathgroup at smc.vnet.net
• Subject: [mg6384] Re: wrong divergence?!?
• From: "Edward G. Neuman" <edneuman at math.siu.edu>
• Date: Sat, 15 Mar 1997 01:21:19 -0500 (EST)
• Organization: Unknown Organization
• Sender: owner-wri-mathgroup at wolfram.com

```
peter <psalzman at landau.ucdavis.edu> wrote in article
<5gagic\$g02 at smc.vnet.net>...
>
> hi all
>
> when i take the divergence of:
>
>   e = {q/r^2, 0, 0}
>
> i get zero.  i remembered to load VectorAnalysis and SetCoordinates to
> Spherical.
>
> this is the electric field due to a point charge at the origin.  even
> though MMA doesn't know maxwell's equations, if we strip all the physical

> meaning from this vector field, shouldn't the divergence be something
other
> than zero at the origin?
>
> thanks!
>
> peter
> --
> Birthdays are good for you:  A federal funded project has recently
determined
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>
>

Function Div returns a correct value. To check it calculate divergence in
spherical coordinates to obtain:

div (q/r^2, 0 , 0) = (1/r^2) * D[(r^2) * (q/r^2), r] = (1/r^2) * D[q,r] =
0.
I assume that q does not depend on r.

I hope this helps.

====================================================
Edward Neuman
E-mail: edneuman at siu.edu
http://www.math.siu.edu/neuman/personal.html

```

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