StackOverflow示例，使用scipy的svd进行PCA：

Albert Au Yeung写的Matrix Factorization 的例子。MF是推荐系统常规算法。

近来做了一些PKI、数字证书方面的东西，对Windows下CryptoAPI和OpenSSL做了一些分析。下图是在一次分享中提到的OpenSSL架构：

#!/usr/bin/env python
# -*- coding: utf-8 -*-
 
'''
file: kd_tree_kNN.py
author: xjump.me#at#gmail#dot#com

REF:
  http://docs.scipy.org/doc/scipy/reference/generated/scipy.spatial.KDTree.html
'''

import numpy as np
import operator
from scipy.spatial import cKDTree as KDTree

import sys
sys.setrecursionlimit(10000)

if __name__=="__main__":
  v0 = np.array([1,2,3,4,5,6])
  train_data_set = np.array([
    [1.2,3,6,7,3,2],
    [2,9,17,7,6,59],
    [1.2,44,6,3,3,23],
    [9,3,51,7,3,100],
    [18,4,39,7,3,21],
    [66,8,28,7,3,88],
    [3,1,2,7,3,33],
    [24,0.5,1,7,3,56],
    [22,99,7,7,3,0.6],
    [70,13,9,7,3,2],
  ])
  tree = KDTree(train_data_set)
  for k in range(1,10):
    print 'k=',k
    #test sample v0, return 3 nearest point, dimesion is k
    print tree.query(v0,k=3,p=k)

算法简单，原理就不介绍了，直接上代码：