Re: Can someone tell me why NDsolve isn't working here?

*To*: mathgroup at smc.vnet.net*Subject*: [mg44040] Re: Can someone tell me why NDsolve isn't working here?*From*: "Eckhard Hennig" <aidev at n-o-s-p-a-m.kaninkolo.de>*Date*: Sun, 19 Oct 2003 01:10:34 -0400 (EDT)*References*: <bmqplo$rhb$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

"Mizrandir" <mizrandir at hotmail.com> schrieb im Newsbeitrag news:bmqplo$rhb$1 at smc.vnet.net... > Hello, Im trying to solve a system of 6 differential equations with > NDSolve but I can't get Mathematica to do it. I wrote: [...] > And Mathematica gave me the following error: > > NDSolve::"ndode": "Input is not an ordinary differential equation." You're getting this error because your equations are of DAE type (differential-algebraic equations) rather than ODE. Unlike ODEs, DAEs involve algebraic (i.e. non-differential) constraints, such as Ry[t] + Fy[t] == 0. NDSolve cannot solve this type of equations, at least for Mathematica versions < 5. You can try to solve your equations with the NDAESolve command from Analog Insydes (www.analog-insydes.de), which has been designed for solving electrical circuit equations. Its trapezoidal integrator may not be ideal for your application though (looks to me like a mechanical system where energy conservation is important). Best regards, Eckhard -- Dr.-Ing. Eckhard Hennig www.kaninkolo.de/ai aidev \at kaninkolo \dot de