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MathGroup Archive 2007

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Re: DSolve y'[t]==y[t-a]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73263] Re: DSolve y'[t]==y[t-a]
  • From: "ben" <benjamin.friedrich at gmail.com>
  • Date: Fri, 9 Feb 2007 02:18:58 -0500 (EST)
  • References: <eqend4$4e6$1@smc.vnet.net>

Hi Peter,

your equation is NOT an ODE, it is an delayed ODE !
That makes a huge difference both in theory and in the numerical
treatment.
There are add-ons available for Mathematica that solve them, look out for
NDelayDSolve.m.
Beware that they can behave quite irregular.
Why not start with a simple Euler scheme, then you can put in your
delay by hand.

Bye
Ben

On 8 Feb., 09:35, Peter Breitfeld <p... at t-online.de> wrote:
> I want to solve the equation in the subject. If I enter
>   DSolve[y'[t] == y[t - a], y[t], t]
> I get the error DSolve::ambiguity.
>
> I triede to define
> k[t]=y[t-a]
> and to solve the resulting system, but this doesn't work either
> because the ambiguity of the independent variable remains.
>
> Any ideas?
>
> Gruss Peter
> --
> ==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==
> Peter Breitfeld, Bad Saulgau, Germany --http://www.pBreitfeld.de




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