financial.py 文件源码

def npv(rate, values):
    """
    Returns the NPV (Net Present Value) of a cash flow series.

    Parameters
    ----------
    rate : scalar
        The discount rate.
    values : array_like, shape(M, )
        The values of the time series of cash flows.  The (fixed) time
        interval between cash flow "events" must be the same as that for
        which `rate` is given (i.e., if `rate` is per year, then precisely
        a year is understood to elapse between each cash flow event).  By
        convention, investments or "deposits" are negative, income or
        "withdrawals" are positive; `values` must begin with the initial
        investment, thus `values[0]` will typically be negative.

    Returns
    -------
    out : float
        The NPV of the input cash flow series `values` at the discount
        `rate`.

    Notes
    -----
    Returns the result of: [G]_

    .. math :: \\sum_{t=0}^{M-1}{\\frac{values_t}{(1+rate)^{t}}}

    References
    ----------
    .. [G] L. J. Gitman, "Principles of Managerial Finance, Brief," 3rd ed.,
       Addison-Wesley, 2003, pg. 346.

    Examples
    --------
    >>> np.npv(0.281,[-100, 39, 59, 55, 20])
    -0.0084785916384548798

    (Compare with the Example given for numpy.lib.financial.irr)

    """
    values = np.asarray(values)
    return (values / (1+rate)**np.arange(0, len(values))).sum(axis=0)