fedoo.constraint.IPCSelfContact.set_start

IPCSelfContact.set_start(pb)

Begin a new time increment.

Kappa management follows the reference IPC algorithm:

1. Re-initialization from gradient balance at each time step when contacts exist. The MAX guard in _initialize_kappa prevents kappa from decreasing.

2. Adaptive doubling — ipctk.update_barrier_stiffness doubles kappa when the gap is small and decreasing. This runs between time steps only (never within the NR loop, as changing kappa mid-solve prevents NR convergence).