calcStayingProb Function

    function calcStayingProb(prob1, prob2, bVal) result(ret)
        ! calculate the probability to stay on a certain excitation branch
        real(dp), intent(in) :: prob1, prob2, bVal
        real(dp) :: ret, tmp
        character(*), parameter :: this_routine = "calcStayingProb"

        ASSERT(prob1 >= 0.0_dp)
        ASSERT(prob2 >= 0.0_dp)
        ASSERT(bVal >= 0.0_dp)

        ! if b == 0 its stupid to use it..
        tmp = max(bVal, 1.0_dp)

        ret = tmp * prob1 / (tmp * prob1 + prob2)

    end function calcStayingProb