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NDSolve in matrix form
*To*: mathgroup at smc.vnet.net
*Subject*: [mg120460] NDSolve in matrix form
*From*: gcarlson <gcarlson at xannah.org>
*Date*: Sun, 24 Jul 2011 03:19:03 -0400 (EDT)
*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com
I am trying to numerically solve systems of ODEs using Mathematica 7.
The desired accuracy that I am striving for depends on the number of
solution functions so I want to structure my solution algorithm to
allow different numbers of solution functions. Solving the problem as
a system of ODEs in matrix form seems the logical choice:
dX/dt = f[X[t]],
where f[X[t]] is a specified function, and X[t] is a vector of
solution functions {x1[t],x2[t],...}. The initial conditions are
specified by a vector X[0] = {x1[0],x2[0],...}.
In my problem, the number of solution functions will usually vary from
3 to 7, but could be any number.
One approach that doesn't work is:
f := {f[[1]][t], f[[2]][t], f[[3]][t]}
fInit := {0, 0, 2}
mat := {(-3*f[[1]][t] - f[[2]][t]), 26.5*f[[1]][t] - f[[2]][t] -
f[[1]][t]*f[[3]][t], f[[1]][t]*f[[2]][t] - f[[3]][t]}
solution = NDSolve[{Derivative[1][f][t] == mat, f[0] == fInit},
f, {t, 0, 17}]
I don't know if the problem is in the way f is specified or in my
expression for NDSolve.
I'd appreciate any assistance.
Thanks and regards,
Glenn
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