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 misleading typo. Best wishes Alois