Re: NDSolve series of ode with equilibrium conditions

*To*: mathgroup at smc.vnet.net*Subject*: [mg21944] Re: NDSolve series of ode with equilibrium conditions*From*: Eckhard Hennig <hennig at itwm.uni-kl.de>*Date*: Sat, 5 Feb 2000 00:49:18 -0500 (EST)*Organization*: ITWM*References*: <87avsu$o1r@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

David Grymonpre schrieb in Nachricht <87avsu$o1r at smc.vnet.net>... > >I am having a problem using NDSolve. I have a series of linear ODE's >such as: > >y1'[t]== f(y1[t], y2[t], ...y40[t]) >. >. >. >y40'[t]== f(y1[t], y2[t], ...y40[t]) > >with initial conditions for each equation. I need to add several >equilibrium equations where one variable is a function of several of the >other variables such as: > >y1[t]=K*y2[t]*y3[t] where K is a constant. > >As of now, the system is quite complex (as far as lines of code for the >problem) and I am trying to find a way to include these equilibrium >equations in my system. The code works when the equilibrium equations >are not included. How do I include the additional equilibrium >equations? I am using version 3.0. David, the system of equations you want to solve is a DAE (differential-algebraic equation) rather than a system of ODE's. Unfortunately, NDSolve cannot handle this type of equations. However, our circuit analysis toolbox Analog Insydes includes a numerical DAE solver (NDAESolve) that may help you to solve your problem. You can download a fully functional demo version from our web site (see my signature). In addition, if you send me your equations, I can show you how to use NDAESolve. Best regards, Eckhard Hennig ----------------------------------------------------------- Dipl.-Ing. Eckhard Hennig mailto:hennig at itwm.uni-kl.de Institut fuer Techno- und Wirtschaftsmathematik e.V. (ITWM) Erwin-Schroedinger-Strasse, 67663 Kaiserslautern, Germany Voice: +49-(0)631-205-3126 Fax: +49-(0)631-205-4139 http://www.itwm.uni-kl.de/as/employees/hennig.html ITWM - Makers of Analog Insydes for Mathematica http://www.itwm.uni-kl.de/as/products/ai -----------------------------------------------------------