word_distance.py 文件源码

def pwdist_kld(self, seq1idx, seq2idx):
        """Kullback-Leibler discrepancy (KL) between two vectors.

        The KL discrepancy between sequences X and Y,
        is computed from their L-tuple (word) frequencies.

        References:
            1. Wu, Hsieh, Li (2001) Biometrics 57: 441-448.
               doi: 10.1111/j.0006-341X.2001.00441.x

        Notes:
            1. KL discrepancy must be computed based on relative
               frequencies (those that sum to 1).
            2. To avoid having an infinite dK L (X, Y) when freqs2 = 0,
               the authors suggest modifying the orifinal formulation
               by adding a unit to both terms of the frequency ratio.

        """
        freqs1 = self[seq1idx] + 1
        freqs2 = self[seq2idx] + 1
        values = freqs1 * np.log2(freqs1 / freqs2)
        value = np.sum(values)
        return value