check_deltas Function

    function check_deltas(this, k) result(t)
        type(LanczosCalcType), intent(inout) :: this
        integer :: k
        logical :: t
        if (k <= this%n_states) then
            t = .false.
            return
        end if
        t = .not. any(abs(this%ritz_values(1:this%n_states) - this%ritz_values_old(1:this%n_states)) > this%convergence_error)
    end function check_deltas