Apply Ben-Israel and Iyigun s Probabilistic D-Clustering (PDC) algorithm for clustering. This implementation is based on: Adi Ben-Israel and Cem Iyigun, "Probabilistic D-Clustering", Journal of Classification 25:5-26 (2008)

对科技期刊引用频次进行排序，通过对引用频次排序，判断科技期刊优劣-Journal Citation Frequency of technology to sort, sorted by frequency of reference to judge the merits of science and technology journals