def _vmf_log(X, kappa, mu):
n_examples, n_features = X.shape<EOL>return np.log(_vmf_normalize(kappa, n_features) * np.exp(kappa * X.dot(mu).T))<EOL>
Computs log(vMF(X, kappa, mu)) using built-in numpy/scipy Bessel
    approximations.

    Works well on small kappa and mu.