def Ohnesorge(L, rho, mu, sigma):
    """Calculates Ohnesorge number, `Oh`, for a fluid with the given
    characteristic length, density, viscosity, and surface tension.

    .. math::
         \\text{Oh} = \\frac{\\mu}{\\sqrt{\\rho \\sigma L }}

    Parameters
    ----------
    L : float
        Characteristic length [m]
    rho : float
        Density of fluid, [kg/m^3]
    mu : float
        Viscosity of fluid, [Pa*s]
    sigma : float
        Surface tension, [N/m]

    Returns
    -------
    Oh : float
        Ohnesorge number []

    Notes
    -----
    Often used in spray calculations. Sometimes given the symbol Z.

    .. math::
        Oh = \\frac{\\sqrt{\\text{We}}}{\\text{Re}}= \\frac{\\text{viscous forces}}
        {\\sqrt{\\text{Inertia}\\cdot\\text{Surface tension}} }

    Examples
    --------
    >>> Ohnesorge(1E-4, 1000., 1E-3, 1E-1)
    0.01

    References
    ----------
    .. [1] Green, Don, and Robert Perry. Perry's Chemical Engineers' Handbook,
       Eighth Edition. McGraw-Hill Professional, 2007.
    """
    return mu / (L * rho * sigma) ** 0.5
