Re: system of nonlinear ODE

*To*: mathgroup at smc.vnet.net*Subject*: [mg23745] Re: system of nonlinear ODE*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Mon, 5 Jun 2000 01:09:39 -0400 (EDT)*Organization*: Universitaet Leipzig*References*: <8gv85p$5mt@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi, a) we can't answer questions about syntax errors when you don't give your input in the mail b) if you have typed > f'''(x)+2.4f(x)f''(x)-0.8(f')**2+z=0 > z''(x)+2.4Pr[f(x)z(x)]'=0 > with z(0)=0, z'(0)=0, f''(0)=0, f(0)=0, f'(10)=0 > it is no wonder that Mathematica dont like the input i) function arguments are typed with [] and *not* with () i.e. f[x], f[0], .. ii) the equation equal is == not the set = operator iii) powers are written as x^n and not in the FORTRAN notation x**n iv) you must always give the arguments of a function to DSolve[], NDSolve[] i. e. (f'[x])^ and *not* (f')^2 v) what is the Pr[] function vi) probably your input should be DSolve[{f'''[x] + 2.4f[x]f''[x] - 0.8(f'[x])^2 + z == 0, z''[x] + 2.4Pr*D[f[x]z[x], x] == 0, z[0] == 0, z'[0] == 0, f''[0] == 0, f[0] == 0, f'[10] == 0}, {f[x], z[x]}, x] c) to type a formula, you should use Mathematica's syntax, you can assume that everyone here understand this Regards Jens Ioanna Pappa wrote: > > Hi > I am trying to solve a system of two nonlinear ordinary differential > equations with initial conditions. > The system > is > f'''(x)+2.4f(x)f''(x)-0.8(f')**2+z=0 > z''(x)+2.4Pr[f(x)z(x)]'=0 > with z(0)=0, z'(0)=0, f''(0)=0, f(0)=0, f'(10)=0 > I use NDSolve end the message that gives me is: > NDSolve::deql: > The first argument must have both an equation and an initial condition. > Can you help me; > Gianna > ipappa at mie.uth.gr