Re: desperate, please help.

*To*: mathgroup at smc.vnet.net*Subject*: [mg27366] Re: desperate, please help.*From*: Bernd Brandt <bernd at bio.vu.nl>*Date*: Thu, 22 Feb 2001 02:25:10 -0500 (EST)*Organization*: VU Biology, Amsterdam, The Netherlands*References*: <97003k$tq@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi, You have several functions defined in the NDSolve body. Mathematica does not know T is a function of x unless you tell this. I have defined all the functions outside the body, introduced functions. For instance Exp (x) is written Exp[x]. I thinkthis is what you meant to do: T[x_] := 330 + 43.3*x F = .9*163; c = 9.3; k[x_] := 31.1Exp[(7906*(T[x] - 360)/(T[x]*360))] r[x_] := -k[x]*c*(1 - (1 + 1/K[x])*x) K[x_] := 3.03*Exp[(-830.3*((T[x] - 333)/(T[x]*333)))] NDSolve[{v'[x] == -F÷r[x], v[0] == 0}, {v}, {x, 0, .7}] {{v -> InterpolatingFunction[{{0., 0.7}}, "<>"]}} Regards, Bernd Thjqase wrote: > I need help numerically solving a differential equation coupled with several > algebraic equations. New to Mathematica. Here's code: > > NDSolve[{v'[x] == -F÷r, T[x] == 330 + 43.3*x, F = .9*163, C == 9.3, > k[x] == 31.1Exp(7906*(T - 360)/(T*360)) > , K[x] == 3.03*Exp(-830.3*((T - 333)/(T*333))), > r[x] == -k*C*(1 - (1 + 1/K)*x), > v[0] == 0}, {v} > , {x, 0, .7}] > > Error code is: > > NDSolve::"deql": "The first argument must have both an equation and an \ > initial condition." > > Any suggestions? What am I doing wrong? My head is sore from banging it against > the wall. > > TIA.