On Tue, Oct 8, 2013 at 2:25 PM, Jed Brown <[email protected]> wrote:
> Christophe Ortiz <[email protected]> writes: > > > On Tue, Oct 8, 2013 at 12:18 AM, Jed Brown <[email protected]> wrote: > > > >> Barry Smith <[email protected]> writes: > >> >> - In this type of problem, which TS scheme is recommended ? > TSARKIMEX ? > >> > > >> > Beats me. > >> > >> ARKIMEX should give you a decent integrator with adaptive error control. > >> Use '-ts_arkimex_type 1bee' to use backward Euler with an > >> extrapolation-based error estimator. > >> > > > > Good to know. I tried TSBEULER but it has constant timestep. > > > > -Is there any other TS with adaptive timestep ? > > TSARKIMEX (nonlinearly implicit) and TSROSW (linearly implicit) have > embedded error estimators and adaptive controllers. > > > -With ARKIMEX, is there a way to control the timestep ? For instance, is > it > > possible to control the max factor between two successive timesteps (dt' > = > > factor*dt), in order to avoid rejections ? > > -ts_adapt_basic_clip <shorten,lengthen> - Admissible decrease/increase in > step size > -ts_adapt_basic_safety <safety> - Safety factor relative to target error > -ts_adapt_basic_reject_safety <rsafety> - Extra safety factor to apply if > the last step was rejected > What are the names of the subroutines to access these options directly within the code ? I see there is TSAdaptSetStepLimits but this is to set the min and max timestep size. > > > - Is it possible to have Cranck-Nicholson > > Crank-Nicolson (spelling) > > > with adaptive timestep ? I tried TSCN but it seems timestep is > > constant. > > What would you use as an error estimator? The same approach as 1bee > could be used to write an extrapolation-based method based on > Crank-Nicolson. Patches welcome if you do this (a simple exercise). > > I recommend using an A-stable ARKIMEX method. > Ok, thanks. > > > - I also tried TSROSW. Seems to work quite well in some cases. How does > it > > compare to ARKIMEX ? > > It is linearly implicit. For problems with sometimes-"stiff" > nonlinearities, ARKIMEX can often take longer time steps. If ROSW is > taking similar step sizes, it should be more efficient. > Good to know. Christophe
