[petsc-users] Suggestions for code with dof >> 1 ?

[Jed Brown]

Christophe Ortiz <christophe.ortiz at ciemat.es> writes:

> On Tue, Oct 8, 2013 at 12:18 AM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
>
>> Barry Smith <bsmith at mcs.anl.gov> 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.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 835 bytes
Desc: not available
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20131008/ea29fb88/attachment.pgp>