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Re: Solving stiff differential equations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg84501] Re: Solving stiff differential equations
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Sat, 29 Dec 2007 20:03:27 -0500 (EST)
  • References: <fl4utf$9vb$1@smc.vnet.net>

Hi,

scale the x[t] value to y[t]=x[t]/M ??
Regards
   Jens

dkjk at bigpond.net.au wrote:
> Hi all,
> 
> I want to solve the following nonlinear ODE
> 
> x'[t] == M - 3 x[t] Sqrt[-M*t + 7/10 + x[t]]
> 
> x[0] == 3/10
> 
> where M is a very large number (~10^43).
> 
> I tried solving this using
> 
> M = 10^43;
> s = NDSolve[{x'[t] == M - 3 x[t] Sqrt[-M t + 7/10 + x[t]],
>    x[0] == 3/10}, x[t], {t, -10, 10}, WorkingPrecision -> 20]
> Plot[Evaluate[x[t] /. s], {t, -10, 10}, PlotRange -> All]
> 
> but I got a lot of errors.  Could anyone please advise how I should go
> about solving this?
> 
> Best regards,
> James
> 


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