Re: Is this solvable using Mathematica?

*To*: mathgroup at smc.vnet.net*Subject*: [mg99117] Re: Is this solvable using Mathematica?*From*: dh <dh at metrohm.com>*Date*: Mon, 27 Apr 2009 05:25:13 -0400 (EDT)*References*: <gsuiqn$dq8$1@smc.vnet.net>

Hi, this system of equations is under determined. You have a second order DEQ in a, what needs 2 equation and 1 first order DEQ in b, what needs another equation. Therefore, you will need 3 equations. Daniel johnboy98105 at yahoo.com wrote: > Supposed you want to define a second order derivative along with your > ODEs. (So you can scale the second order term) > > Example shown below. > > k1 = 1; > r1 = 1; > NDSolve[{a'[t] == k1 b[t] - d, a''[t] == r1 b'[t], a'[0] == 0, a[0] == > 1, b[0] == 0}, {a[t], b[t]}, {t, 1, 10} ] > > But I get an error. > > NDSolve::ntdvmm: > Cannot solve to find an explicit formula for the derivatives. NDSolve > will try solving the system using a mass matrix method. > > NDSolve::ndnum: Encountered non-numerical value for a derivative at t > == 0.`. > > Maybe this is more of a math question than software. But I would be > very interested in seeing if it's doable in Mathematica. > > Thanks in advance. > >