Function lsqr_matlab 

pub fn lsqr_matlab<F, G>(
    apply_a: F,
    apply_ah: G,
    b: &[Complex64],
    tol: f64,
    max_iter: usize,
) -> (Vec<Complex64>, LsqrOutcome)
where
    F: FnMut(&[Complex64]) -> Vec<Complex64>,
    G: FnMut(&[Complex64]) -> Vec<Complex64>,

LSQR (Paige & Saunders 1982) with MATLAB lsqr’s stopping rules, zero initial guess, no preconditioner: stops when ‖r‖ ≤ tol·‖b‖ or ‖Aᴴr‖ / (‖A‖_F·‖r‖) ≤ tol (both tested on the previous iterate, before it is updated), after three stagnant steps, or on breakdown. apply_a computes A x, apply_ah computes Aᴴ u.