Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
1997
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 1997

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: wrong divergence?!?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg6384] Re: wrong divergence?!?
  • From: "Edward G. Neuman" <edneuman at math.siu.edu>
  • Date: Sun, 16 Mar 1997 19:24:48 -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
> that people with the most number of birthdays will live the longest.....
>
-=><=-+-+-=><=-+-+-=><=-+-+-=><=-+-+-=><=-+-+-=><=-+-+-=><=-+-+-=><=-+-+-=><
=-
>      I BOYCOTT ANY COMPANY THAT USES MASS ADVERTISING ON THE INTERNET
> 
> 
> 

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


  • Prev by Date: Re: Numerical Left Eigenvectors
  • Next by Date: How do I use BooleanSelect?
  • Previous by thread: Re: wrong divergence?!?
  • Next by thread: Re: Re: wrong divergence?!?