r'''Returns the volume of a hollow cylinder.

    .. math::
        V = \frac{\pi D_o^2}{4}L - L\frac{\pi D_i^2}{4}

    Parameters
    ----------
    Di : float
        Diameter of the hollow in the cylinder, [m]
    Do : float
        Diameter of the exterior of the cylinder, [m]
    L : float
        Length of the cylinder, [m]

    Returns
    -------
    V : float
        Volume [m^3]

    Examples
    --------
    >>> V_hollow_cylinder(0.005, 0.01, 0.1)
    5.890486225480862e-06

def V_hollow_cylinder(Di, Do, L):
    r'''Returns the volume of a hollow cylinder.

    .. math::
        V = \frac{\pi D_o^2}{4}L - L\frac{\pi D_i^2}{4}

    Parameters
    ----------
    Di : float
        Diameter of the hollow in the cylinder, [m]
    Do : float
        Diameter of the exterior of the cylinder, [m]
    L : float
        Length of the cylinder, [m]

    Returns
    -------
    V : float
        Volume [m^3]

    Examples
    --------
    >>> V_hollow_cylinder(0.005, 0.01, 0.1)
    5.890486225480862e-06
    '''
    V = pi*Do**2/4*L - pi*Di**2/4*L
    return V