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MathGroup Archive 2000

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Re: NDSolve error message: Can't find starting value ...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg23768] Re: NDSolve error message: Can't find starting value ...
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Sat, 10 Jun 2000 02:59:14 -0400 (EDT)
  • Organization: Universitaet Leipzig
  • References: <8hfggl$i4h@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

for a second order equation you have to supply the 
function value R[x] *and* the first dervative R'[x],
or R[x1] and R[x2] ...
but never a second derivatives like R''[-3].

NDSolve[] will not able to solve a equation with a
DiracDelta[] function because the numerical methods
require Lipschitz continuous right hand sides.

You should have a look in some undergraduate mathematics
books *before* you use Mathematica.

Regards
  Jens

Axel Kowald wrote:
> 
> Hello,
> 
> I try to solve the following second order ODE with NDSolve
> 
> NDSolve[{0 == R''[x] + DiracDelta[x] - R[x],         R''[-3] == 0,
> R''[3] == 0}, R, {x, -3, 3}]
> 
> and I get the following error message:
> 
> NDSolve::"ndsv": "Cannot find starting value for the variable x."
> 
> I couldn't find any description of this message in the Mathematica book, so I'm
> not sure what to do. I have a second order ODE with two boundary
> conditions, what's missing ?
> 
> Many thanks,
> 
>                Axel Kowald
> 
> P.S. Btw., this is done with Mathematica 4.


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