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MathGroup Archive 2000

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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


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