shared.py 文件源码

def median_heuristic(y):
    """  Estimate RBF bandwith using median heuristic. 

    Parameters
    ----------
    y : (number of samples, dimension)-ndarray
        One row of y corresponds to one sample.

    Returns
    -------
    bandwidth : float
                Estimated RBF bandwith.

    """

    num_of_samples = y.shape[0]  # number of samples
    # if y contains more samples, then it is subsampled to this cardinality
    num_of_samples_used = 100

    # subsample y (if necessary; select '100' random y columns):
    if num_of_samples > num_of_samples_used:
        idx = choice(num_of_samples, num_of_samples_used, replace=False)
        y = y[idx]  # broadcasting

    dist_vector = pdist(y)  # pairwise Euclidean distances
    bandwith = median(dist_vector) / sqrt(2)

    return bandwith