On 24 March 2015 at 06:15, Emil Constantinescu <emcon...@mcs.anl.gov> wrote: > On 3/23/15 4:44 AM, Lisandro Dalcin wrote: > > Lisandro, that's a neat idea. If you are basically moving in the multistep > realm for error estimation with one-step methods,
I'm wondering if no one ever did it. I could not find any reference. > I think there are two > considerations: > > 1. The equations need to be continuous (no restarting, no events) or they > would have to reset the error estimator somehow. > Indeed. My generalized-alpha code does not handle events at all. I'll take a look into this. About restarting (not sure if we are talking about the same thing), I have some code that is specific to generalized-alpha (In the initial time step, I solve twice with backward-Euler using dt/2 and dt) that let me properly initialize generalized-alpha and also compute an initial error estimator. > 2. Backward differences are sensitive to time stepping changes; unlike > one-step methods that can accommodate any step changes, B-D has strict > limits for stability. While this does not play a crucial role (it is just > the estimator); Of course, though my B-D is order 2, and as you said, it is the just for the estimator. > if the time step varies wildly (can be easily constrained), > it may create some problems with the estimator. > Indeed, the default clipping 0.1,10 is usually too wide, I usually do -ts_adapt_basic_clip 0.5,2.0 Emil, is there any chance you can try my code with your problem? I really need some feedback to push this to PETSc, otherwise -- Lisandro Dalcin ============ Research Scientist Computer, Electrical and Mathematical Sciences & Engineering (CEMSE) Numerical Porous Media Center (NumPor) King Abdullah University of Science and Technology (KAUST) http://numpor.kaust.edu.sa/ 4700 King Abdullah University of Science and Technology al-Khawarizmi Bldg (Bldg 1), Office # 4332 Thuwal 23955-6900, Kingdom of Saudi Arabia http://www.kaust.edu.sa Office Phone: +966 12 808-0459