Re: NDSolve precision and velocity problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg91312] Re: NDSolve precision and velocity problem*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Fri, 15 Aug 2008 06:52:44 -0400 (EDT)*Organization*: The Open University, Milton Keynes, UK*References*: <g81378$o$1@smc.vnet.net>

Joerg Schaber wrote: > I have an ODE system that takes lots of time to solve with NDSolve > (several minutes), > whereas the same system with the FORTRAN solver LSODA > solves the problem in an second. > When I decrease the precision, e.g. AccuracyGoal->6, NDSolve crashes. It > often crashes, because it finds complex values in a less-than-comparison. > > Maybe it's a method problem. > How do I tell NDSolve, to use the same methods as the LSODEA solver? If by the above you mean using either Adams or Backward Differentiation Formula (BDF) methods [1], for nonstiff or stiff cases, respectively, you can use the option *Method*. The following might be worth reading (or at least browsing): [2, 3, 4] Regards, - Jean-Marc [1] "LSODE", _Serial Fortran Solvers for ODE Initial Value Problems_, https://computation.llnl.gov/casc/odepack/odepack_home.html [2] _IDA Method for NDSolve_, http://reference.wolfram.com/mathematica/tutorial/NDSolveIDAMethod.html [3] "Adams methods", _NDSolve Method Plug-in Framework_, http://reference.wolfram.com/mathematica/tutorial/NDSolvePlugIns.html [4] _Monitoring and Selecting Algorithms_, http://reference.wolfram.com/mathematica/tutorial/MonitoringAndSelectingAlgorithms.html