def check_termination(dF, F, dx_norm, x_norm, ratio, ftol, xtol):
    """Check termination condition for nonlinear least squares."""
    ftol_satisfied = dF < ftol * F and ratio > 0.25
    xtol_satisfied = dx_norm < xtol * (xtol + x_norm)

    if ftol_satisfied and xtol_satisfied:
        return 4
    elif ftol_satisfied:
        return 2
    elif xtol_satisfied:
        return 3
    else:
        return None