def perf_index(X, base=100., axis=0, dtype=None):
    """ Compute performance of prices or index values along time axis.

    Parameters
    ----------
    X : np.ndarray[dtype, ndim=1 or 2]
        Time-series of prices or index values.
    base : float, optional
        Initial value for measure the performance, default is 100.
    axis : {0, 1}, optional
        Axis along wich the computation is done. Default is 0.
    dtype : np.dtype, optional
        The type of the output array.  If `dtype` is not given, infer the data
        type from `X` input.

    Returns
    -------
    np.ndarray[dtype, ndim=1 or 2]
        Performances along time axis.

    See Also
    --------
    perf_returns, perf_strat

    Examples
    --------
    >>> X = np.array([10., 12., 15., 14., 16., 18., 16.])
    >>> perf_index(X, base=100.)
    array([100., 120., 150., 140., 160., 180., 160.])

    """
    return base * X / X[0]