Re: Multiple St.St. and Alg-Diff Eq
- To: mathgroup at smc.vnet.net
- Subject: [mg23115] Re: Multiple St.St. and Alg-Diff Eq
- From: Eckhard Hennig <hennig at itwm.uni-kl.de>
- Date: Wed, 19 Apr 2000 02:30:47 -0400 (EDT)
- Organization: ITWM
- References: <8d9758$iih@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Sharon Smith schrieb in Nachricht <8d9758$iih at smc.vnet.net>... >Two questions: > >1) Can Mathematica solve for multiple steady states? Currently I am using >Findroot and am getting solutions seem to oscillate between 2 different >steady states. Sharon, since you mentioned the function FindRoot, I assume that what you are referring to is the initial solution of a set of differential equations at t = 0 or, in terms of circuit analysis, the DC operating point. The term "(periodic) steady state" usually refers to the response of a system to a (periodic) input signal as t approaches infinity, that is after all influences of initial conditions have vanished. OK, back to your question: If you encounter oscillations when trying to find a DC OP using FindRoot, you can try the following. * play with the FindRoot option DampingFactor * try different initial values (for instance, by adding random noise) * use the secant method instead of the Newton-Raphson method However, there is no guarantee that the above approaches will be successful. >2) Can Mathematica solve systems of Algebraic and Differential Equations >(i.e. like DASSL)? No, not in the general case. If you need a DAE solver, you may want to try the package NDAESolve which is part of the circuit analysis toolbox Analog Insydes. There's a free demo version available from www.itwm.uni-kl.de/as/products/ai or from MathSource. Best regards, Eckhard ----------------------------------------------------------- Dr.-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 -----------------------------------------------------------