Re: populating a list from system of odes

*To*: mathgroup at smc.vnet.net*Subject*: [mg45933] Re: populating a list from system of odes*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Fri, 30 Jan 2004 04:16:00 -0500 (EST)*Organization*: Universitaet Leipzig*References*: <bvaq98$ah0$1@smc.vnet.net>*Reply-to*: kuska at informatik.uni-leipzig.de*Sender*: owner-wri-mathgroup at wolfram.com

Hi, you mean eqn = {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]}; Union[Cases[eqn, _[t], Infinity]] /. a_Derivative[_][_] :> Sequence[] Regards Jens sean kim wrote: > > 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