def P_stagnation(P, T, Tst, k):
    """Calculates stagnation flow pressure `Pst` for a fluid with the
    given isentropic coefficient and specified stagnation temperature and
    normal temperature. Normally used with converging/diverging nozzles.

    .. math::
        \\frac{P_0}{P}=\\left(\\frac{T_0}{T}\\right)^{\\frac{k}{k-1}}

    Parameters
    ----------
    P : float
        Normal pressure of a fluid [Pa]
    T : float
        Normal temperature of a fluid [K]
    Tst : float
        Stagnation temperature of a fluid moving at a certain velocity [K]
    k : float
        Isentropic coefficient []

    Returns
    -------
    Pst : float
        Stagnation pressure of a fluid moving at a certain velocity [Pa]

    Notes
    -----
    Assumes isentropic flow.

    Examples
    --------
    Example 12-1 in [1]_.

    >>> P_stagnation(54050., 255.7, 286.8, 1.4)
    80772.80495900588

    References
    ----------
    .. [1] Cengel, Yunus, and John Cimbala. Fluid Mechanics: Fundamentals and
       Applications. Boston: McGraw Hill Higher Education, 2006.
    """
    return P * (Tst / T) ** (k / (k - 1.0))
