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MathGroup Archive 2004

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Re: numerical solution of an ODE doesn't make sense

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49531] Re: numerical solution of an ODE doesn't make sense
  • From: Alois Steindl <Alois.Steindl at tuwien.ac.at>
  • Date: Fri, 23 Jul 2004 05:59:20 -0400 (EDT)
  • References: <cdnqcj$l61$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

"Ita" <kitamar at actcom.net.il> writes:

> Hello, and thanks in advance to any response.
> I solved a 2nd degree ode with NDSolve for the unknown x(t) for 2 time
> domains: 0<t<100 and 0<t<700, with the same boundary conditions.
> than I ploted the two solutions for 0<t<20, and they came out different ! it
> is like the solution in t<20 is influenced by the solution in t>100 - it
> doesn't make sense.
> thanks,
> Itamar.

Hello,
this certainly depends on the differential equation and the boundary
conditions! 
Consider the simple problem
u'' = -1
u(0) = 0
u'(L) =0
(this might model the longitudinal deformation of an elastic rod under
constant axial load).
The solution strongly depends on L.
Alois
 


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