How do you change the desired accuracy of a TS object in PETSc?

I'm currently getting very long propagation times when attempting to use the Time Stepping propagators in Petsc 3.2, and in the interest of speeding things up, I'm curious how I can reduce the accuracy (or see what it is in the first place) to speed it up.

• Are you solving a linear or nonlinear system of equations at each time step? – Aron Ahmadia May 2 '12 at 6:22
• Linear, is TS for linear propagation? or just for non-linear propagation. – Andrew Spott May 2 '12 at 19:46

nonlinear systems of equations

In general, the PETSc TS propagators solve a nonlinear system of equations at each time step, so you would need to access the SNES object and modify its accuracy tolerance there. See the documentation on SNESSetFromOptions for a list of the command line options available to you for adjusting the solver tolerances.

linear system of equations

PETSc doesn't expose the KSP object belonging to TS in the same way at the command-line, @JedBrown or @MattKnepley may be able to comment on why. Programmatically, you can:

TSGetKSP(ts, &ksp);

KSPSetTolerances(ksp, rtol, abstol, dtol, maxits;

• What about for a linear system of equations? – Andrew Spott May 2 '12 at 20:44