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 > - 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. > - 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.
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