Tianchan Niu <niu <at> isis.georgetown.edu> writes: > > Dear All, > > I was using rk4 and lsoda to solve a ODE system. However, both of them gave > bad accurate solutions, especially compared with Matlab solver ODE45. For > example, ODE45 gave solutions that can go to a stable level (about 1.6) when > time goes to infinity, however, the solutions from lsoda are decreasing to > very very small (about 1e-130) numbers. > > Does R have more accurate ODE solvers as ODE45 in Matlab?
See ?rkMethods in the deSolve package. You could try rk(..., method="ode45") or otherwise try playing with the tolerances. Without a reproducible example, it's pretty much impossible to say what the precise problem is. It's mildly surprising (although I am *not* a numerical analyst) that the default 'lsoda' solver doesn't work well. At least in the general description of the algorithm, method="ode45" is the same as MATLAB's algorithm, although it's entirely possible that the default tolerances, details of the implementation, etc., have been tuned differently in the two packages (since MATLAB is closed-source, we can't tell what the precise details are). It would be interesting to know where the actual problem lies (different tolerance setting, ode45 vs lsoda, MATLAB vs R implementation); can you report on your findings and/or post a reproducible example? ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
