设X为一个随机生成的2行4列的矩阵，求X的相关矩阵
numpy库有多种方法：
>>> import numpy as np
>>> np.random.rand(2,4)
array([[0.20967727, 0.90905959, 0.54781651, 0.2993528 ],
[0.32707425, 0.47562761, 0.97902248, 0.74274156]])
>>> np.random.random(size=(2,4))
array([[0.97192929, 0.40497475, 0.85808984, 0.26553934],
[0.94609003, 0.44717649, 0.82243045, 0.81606412]])
>>> np.random.randint(1,100,size=(2,4))
array([[ 4, 80, 56, 9],
[92, 9, 6, 38]])
>>>