Note that BDF has the same issue. I think the correct way to handle this is to support storing/loading these extra vectors via TSView()/TSLoad(). How are you currently restarting the simulation? Il giorno gio 2 gen 2025 alle ore 19:25 David Kamensky via petsc-users < [email protected]> ha scritto:
Hi,
I've recently been helping some co-workers with restarting PETSc time integrators from saved solution data.
It looks like the only supported path for restarting the generalized-alpha integrator for 2nd-order-in-time systems (`TSALPHA2`) is to follow the same procedure as initialization, in which two first-order-accurate half-steps are used to estimate an acceleration from the given displacement and velocity. However, the resulting acceleration is not exactly equivalent to the intermediate one that would have been used by the integrator if the integration simply proceeded without restarting. This prevents exact reproducibility of computations from saved intermediate results. (An analogous issue would also affect `TSALPHA` for first-order-in-time problems, where velocity is estimated on initialization/restart.)
Am I misunderstanding this, or missing a better method of restarting the 2nd-order generalized-alpha integrator? If not, would there be interest in adding an alternate initialization/restart option to the `TSALPHA2` integrator that takes a user-provided `Vec` for the initial/intermediate acceleration, and skips over the half-step estimation procedure?
Thanks, David
-- Stefano