sampler.py 文件源码

def chin(self):
        """approximation of the expected length.

        The exact value could be computed by::

            from scipy.special import gamma
            return 2**0.5 * gamma((self.dimension+1) / 2) / gamma(self.dimension / 2)

        The approximation obeys ``chin < chin_hat < (1 + 5e-5) * chin``.

        """
        values = {1: 0.7978845608028656, 2: 1.2533141373156,
                  3: 1.59576912160574,   4: 1.87997120597326}
        try:
            val = values[self.dimension]
        except KeyError:
            # for dim > 4 we have chin < chin_hat < (1 + 5e-5) * chin
            N = self.dimension
            val = N**0.5 * (1 - 1. / (4 * N) + 1. / (26 * N**2)) # was: 21
        return val