Function sequential_run 

pub fn sequential_run<T, S>(
    state: &mut [T],
    options: &Options,
    step: &S,
) -> (usize, bool)
where
    T: Copy,
    S: Step<T>,

Sequential Gauss-Seidel execution: roots are updated in-place in ascending index order within each iteration (later roots see earlier updates).

Converged roots contribute a zero tolerance and are not written; their values stay frozen as neighbors for the remaining sweeps.