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MathGroup Archive 1999

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Re: newbie Mathematica question (astrophysics problem)

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18304] Re: newbie Mathematica question (astrophysics problem)
  • From: Attico Nicola <attico at cibs.sns.it>
  • Date: Fri, 25 Jun 1999 22:24:13 -0400
  • Organization: Universita' di Pisa
  • References: <7l0lb6$cts@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On 25 Jun 1999, Alexander Sirotkin wrote:

> [Contact the author to obtain details - moderator]
> 
> Hi.
> 

Hi.

> I'm trying to solve system of differential equations from 
> astrophysics. 
> 

I also, not from astrophysics but from plasma physics
but i think is nearly the same!

> It appears that I have made some mysterious mistake in mathematica
> code, but I have no idea where since all mathematica error 
> messages are absolutely non-informative.
> 
> Anybody can take a look ?
> 
> P.S.
> 
> I get the following errors:
> Possible spelling 
>   error: new symbol name "diffEqP" is similar to existing symbol
> "diffEqM".
> 

I think it's not really an error.
This happens whene you are using two simbols that
have very similar names (as in your case).
Tipically if you run two times the same command the "error"
disappears.

> NDSolve::"ndnum": 
>     "The right-hand side of the differential equation does not evaluate to
> a \
> number at r == 0.`.
> 

This is not clear and i think this is the true error.
I see you are using the package NDSolve.
Maybe the differential equation you are studing
have  a singuarity in r=0 (galaxies? sometimes ago i was studying
accretion disks! :)
If its not too complex post more details in the newsgroup.
I think this problem can interest a lot of people.

PS. Have you tried with DSolve?

Bye

Nicola


-----
Nicola Attico
(attico at cibs.sns.it)




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