[petsc-users] PETSC TS Extrapolation

Zhang, Hong hongzhang at anl.gov
Wed Dec 15 12:44:58 CST 2021

On Dec 14, 2021, at 2:18 PM, Alfredo J Duarte Gomez <aduarteg at utexas.edu<mailto:aduarteg at utexas.edu>> wrote:

Hello PETSC team,

I have some questions about the extrapolation routines used in the TS solvers.

I wish to use an extrapolation as the initial guess for the solution at the next time step, which should have an order equivalent to the order of my TS solver.

So far, I have been using the TS THETA with the extrapolate flag, but it is also my understanding that the TS BDF extrapolates by default.

What values are used in these extrapolation routines? Is it the derivative plus k solutions (where k is the order of the extrapolation) or is it k+1 previous solutions?

Looking at the function TSBDF_Extrapolate(), I think it is the latter.

I am also unsure about what happens at the boundaries when using DAEs. Are the values at the boundaries extrapolated as well? Or is there no extrapolation at the boundary points?

All the values in the solution vector will be extrapolated. So the boundary values are extrapolated as soon as they are included in the vector.

Hong (Mr.)

Thank you,


Alfredo Duarte
Graduate Research Assistant
The University of Texas at Austin

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