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MathGroup Archive 2004

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Re: solving for variable and then get these e's..?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg46931] Re: solving for variable and then get these e's..?
  • From: Gregor Pfyffer <g.pfyffer at oma.be>
  • Date: Tue, 16 Mar 2004 19:54:56 -0500 (EST)
  • References: <c33de2$ftc$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

I found your error! You don't assign a random value to the variable e 
you define in In[270], but therfore you twice dfine a value to d ! I 
assume this to be a copy-paste error. ;-))

Kind regards
Gregor

sean kim wrote:
> Hello Group. 
> 
> I was playing around with lorenz system again. I assigned random
> numbers for all the parameters. and made a steady state system based
> on that and solved for the variables. and I get the following. ( the
> code is at the bottom)
> 
> {y[0] == 0.1889025652295933*(-1.3382047869208344 - 
>      0.47590327034877034*Sqrt[7.906927918602607 - 
>         18.515309886236974*e]), 
>   x[0] == 0.31792235868739005*(1.5727110293983604 + 
>      0.5593002876087739*Sqrt[7.906927918602607 - 
>         18.515309886236974*e]), 
>   z[0] == 0.042970475451898735*(7.906927918602607 + 
>      2.8119260158479644*Sqrt[7.906927918602607 - 
>         18.515309886236974*e]}
> 
> What are those little e's at the end of the solutions? Is that euler's
> number? and why can't I use that in NDSolve routine? are those
> signifcant?
> 
> any thoughts are appreciated.
> 
> In[270]:=
> ode = {x'[t]== -a y[t]-b z[t],y'[t]== c x[t]+d y[t],
>     z'[t] == e-f z[t]+f x[t] z[t]}
> 
> %/._'[t]->0
> 
> Solve[%,{x[t], y[t], z[t]}]
> 
> %/.{a-> Random[Real, {1, 3}], b-> Random[Real, {1, 3}],
> c-> Random[Real, {1, 3}],d-> Random[Real, {1, 3}],
> d-> Random[Real, {1, 3}],f-> Random[Real, {1, 3}]}/.Rule ->Equal/.t->
> 0 //InputForm
> 
> s1 =% [[1]]
> s2 = %%[[2]]
> 
> NDSolve[Join[{x'[t]\[Equal]-a y[t]-b z[t],y'[t]\[Equal]c x[t]+d y[t],
>       z'[t]\[Equal]e-f z[t]+f x[t] z[t]}, s1], {x[t], y[t], z[t]}, {t,
> 0, 10}]
> 


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