numpy库

1、创建随机矩阵

>>> from numpy import *
>>> random.rand(4,4)
array([[ 0.1801566 ,  0.02580119,  0.02685281,  0.52768083],
       [ 0.45411008,  0.7831068 ,  0.21375316,  0.5834276 ],
       [ 0.14515285,  0.56107743,  0.70939684,  0.38059215],
       [ 0.38190561,  0.90318702,  0.36228335,  0.41596983]])
>>> random.rand(1,5)
array([[ 0.44651467,  0.62156783,  0.26844721,  0.0429569 ,  0.94402983]])
>>> mat(random.rand(2,2))-----》转换为矩阵
matrix([[ 0.70740332,  0.74586087],
        [ 0.63854925,  0.08342785]])
>>> randMat = mat(random.rand(4,5))
>>> randMat
matrix([[ 0.06601757,  0.01608014,  0.42190585,  0.01011915,  0.31645594],
        [ 0.65403083,  0.59347221,  0.19135569,  0.46777104,  0.66128351],
        [ 0.35348795,  0.82899244,  0.56450194,  0.90785287,  0.79258663],
        [ 0.71413199,  0.62240897,  0.17560023,  0.51640713,  0.51107191]])
>>> randMat.I-----》求矩阵的逆
matrix([[ 0.99798378, -1.76149543, -1.19227532,  3.46560494],
        [-0.85138719, -0.19618883,  0.49031565,  0.21072417],
        [ 2.50529117, -4.01838827,  0.18836154,  3.3826735 ],
        [-0.89262193, -1.69025782,  1.0541609 ,  0.95941787],
        [-0.31650047,  5.78889385, -0.06102358, -5.27421759]])
>>>
>>> IrandMat = randMat.I
>>> myEye = IrandMat * randMat----》矩阵*矩阵的逆=单位矩阵
>>> myEye
matrix([[ 0.96725654,  0.13928549,  0.01950231, -0.1066253 , -0.02283814],
        [ 0.13928549,  0.40750154, -0.08295973,  0.45356717,  0.09714986],
        [ 0.01950231, -0.08295973,  0.98838424,  0.06350702,  0.01360261],
        [-0.1066253 ,  0.45356717,  0.06350702,  0.65278699, -0.07436979],
        [-0.02283814,  0.09714986,  0.01360261, -0.07436979,  0.98407068]])
>>> myEye - eye(4)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: operands could not be broadcast together with shapes (5,5) (4,4)
>>> eye(4)
array([[ 1.,  0.,  0.,  0.],
       [ 0.,  1.,  0.,  0.],
       [ 0.,  0.,  1.,  0.],
       [ 0.,  0.,  0.,  1.]])
>>> myEye - eye(4)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: operands could not be broadcast together with shapes (5,5) (4,4)
>>> myEye - eye(5)-----》减去5*5的单位矩阵，计算误差
matrix([[-0.03274346,  0.13928549,  0.01950231, -0.1066253 , -0.02283814],
        [ 0.13928549, -0.59249846, -0.08295973,  0.45356717,  0.09714986],
        [ 0.01950231, -0.08295973, -0.01161576,  0.06350702,  0.01360261],
        [-0.1066253 ,  0.45356717,  0.06350702, -0.34721301, -0.07436979],
        [-0.02283814,  0.09714986,  0.01360261, -0.07436979, -0.01592932]])

2、shape()—>针对矩阵

from numpy import *
import operator

print eye(4);
print eye(4).shape;
print eye(4).shape[0];#行数
print eye(4).shape[1];#列数

a = [[1,2,4,5],[2,4,5,5]];
b = mat(a);
print b.shape;
print b.shape[0];
print b.shape[1];
[[ 1.  0.  0.  0.]
 [ 0.  1.  0.  0.]
 [ 0.  0.  1.  0.]
 [ 0.  0.  0.  1.]]
(4, 4)
4
4
(2, 4)
2
4

3、矩阵的重复

c = [1,2];
print tile(c,3);#列重复3次
print tile(c,(2,3));#行重复2次 列重复3次

4、sum()

b = [[1,2,4,5],[2,4,5,5]];
#b = mat(a);
result = np.sum(b,axis=1);#一个矩阵的每一行向量相加，
result2 = np.sum(b,axis=0);#矩阵的所有行向量相加，
print result;
print result2;