For TSBEULER (the theta method) see https://petsc.org/release/docs/manualpages/TS/TSTHETA.html <https://petsc.org/release/docs/manualpages/TS/TSTHETA.html> and look at the source code src/ts/impls/implicit/theta/teta.c for TSStep_Theta. You can use -snes_monitor_solution OPTIONS to see what the solutions are the nonlinear system look like as it solves the system.
Barry > On Oct 11, 2021, at 12:26 PM, Alfredo J Duarte Gomez <[email protected]> > wrote: > > Good morning PETSC team, > > I have a working algorithm for my implicit TS integrator with a system of > ODE/DAE's, but I am observing a rather high number of iterations > > I am currently using the simplest settings of a TSBEULER and setting a > constant time step. > > My question right now is whether the default settings use any sort of > initial guess algorithm before every time step. > > Since I have seen that the time step adapter calculates the Local Truncation > Error, it should be possible to use an extrapolation of arbitrary order of > accuracy as an initial guess for every time step right? Can someone indicate > how I would be able to use that? > > Additionally, it would be very helpful to take a look at that initial guess, > is it possible to use any existing function to calculate it either in the > PreStep or PostStep function to visualize it? > > Thank you, > > -- > Alfredo Duarte > Graduate Research Assistant > The University of Texas at Austin
