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MathGroup Archive 2004

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populating a list from system of odes

  • To: mathgroup at smc.vnet.net
  • Subject: [mg45925] populating a list from system of odes
  • From: sean_incali at yahoo.com (sean kim)
  • Date: Thu, 29 Jan 2004 05:36:54 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

hello group. 

thanks all for the replies. they have been tremendiously helpful. 

(about rossler vz lorenz. you are right, jens. what i did was to copy
the first system that had attractor from the help menu.  lol)

let's say you have a system of ode's like.. 

{
a'[t] == k7 - k5 a[t] + k2 ab[t] - k1 a[t] b[t],
ab'[t] == -k2 ab[t] + k1 a[t] b[t],
b'[t] == k8 + k2 ab[t] - k6 b[t] - k1 a[t] b[t],
c'[t] == k3 ab[t] - k4 c[t]
}

now what I want to do is get a list of the  variables in the system
without having to type them out.

so that I would get {a[t],ab[t], b[t], c[t]}

as you can see from my previous posts, the problems i'm having are
very similar.  I'm sur eit has to do with no tunderstanding the
fundamentals of mathematica... but meanwhile, how would you guys
approach that problem above?

once i have that, i can change the system to steady state easily with 

% /. _'[t] -> 0

which gives 

{
0 == k7 - k5 a[t] + k2 ab[t] - k1 a[t] b[t],
0 == -k2 ab[t] + k1 a[t] b[t],
0 == k8 + k2 ab[t] - k6 b[t] - k1 a[t] b[t],
0 == k3 ab[t] - k4 c[t]
}

which i can use with the list i'm tryign to populate in Solve[]
routine which then can be used in NDSolve[] with the codes you guys
explained.

thank you all very much in advance. 

sean


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