Re: NDSolve, three 2-d order ODE, 6 initial conditions

• To: mathgroup at smc.vnet.net
• Subject: [mg115261] Re: NDSolve, three 2-d order ODE, 6 initial conditions
• From: Alois Steindl <Alois.Steindl at tuwien.ac.at>
• Date: Wed, 5 Jan 2011 05:48:45 -0500 (EST)
• References: <ig0bpr\$s90\$1@smc.vnet.net>

```DrMajorBob <btreat1 at austin.rr.com> writes:

> You're saying, I think, that the following relationship reduces the
> differential order of the system to 5??
>
> Solve[0 ==
>    2 (Sin[5 t] Derivative[1][x][t] - Cos[2 t] Derivative[1][y][t]),
>   y'[t]]
>
> {{Derivative[1][y][t] -> Sec[2 t] Sin[5 t] Derivative[1][x][t]}}
>
> Bobby
>
Yes, the OP wanted to solve a system of 3 second order equations, but
since he left out the argument [t] of z, the lhs of the 3rd equation
vanished and the order dropped by one. (z'[t] is present in the first
equations). This error could be easily detected by looking closely at
the anwer from Mathematica.
I am somewhat angry, that the OP just stated an incomplete problem (he
could have at least provided a sample call to ndSol and cited the error
message, so one would have a better idea what went wrong.) with a