Serial Newton + banded-solve body for BDF2 (including the backward-Euler bootstrap path). Operates entirely on state%ub / state%bdf2_ub_prev / state%resid at whatever size state%decomp%n_local says. Does NOT call compute_resid_glob — the wrapper does, from every rank, after restore_local_layout.
| Type | Intent | Optional | Attributes | Name | ||
|---|---|---|---|---|---|---|
| type(solver_state_t), | intent(inout) | :: | state |