NumPy 教程第 15 章：算术函数

NumPy 算术函数包含简单的加减乘除: add()，subtract()，multiply() 和 divide()

需要注意的是数组必须具有相同的形状或符合数组广播规则

In [1]: import numpy as np

In [2]: x = np.arange(9,dtype = np.float_).reshape(3,3)

In [3]: x
Out[3]:
array([[0.,1.,2.],[3.,4.,5.],[6.,7.,8.]])

In [4]: y = np.array([10,10,10])

In [5]: y
Out[5]: array([10,10])

In [6]: np.add(x,y)
Out[6]:
array([[10.,11.,12.],[13.,14.,15.],[16.,17.,18.]])

In [7]: np.subtract(x,y)
Out[7]:
array([[-10.,-9.,-8.],[ -7.,-6.,-5.],[ -4.,-3.,-2.]])

In [8]: np.multiply(x,y)
Out[8]:
array([[ 0.,10.,20.],[30.,40.,50.],[60.,70.,80.]])

In [9]: np.divide(x,y)
Out[9]:
array([[0.,0.1,0.2],[0.3,0.4,0.5],[0.6,0.7,0.8]])

numpy.reciprocal() 函数

返回参数逐元素的倒数，如 1/4 倒数为 4/1

In [1]: import numpy as np

In [2]: num = np.array([0.25,1.33,1,100])

In [3]: num
Out[3]: array([  0.25,100.  ])

In [4]: np.reciprocal(num)
Out[4]: array([4.,0.7518797,0.01     ])

numpy.power() 函数

将第一个输入数组中的元素作为底数，计算它与第二个输入数组中相应元素的幂

In [1]: import numpy as np

In [2]: x = np.array([10,100,1000])

In [3]: x
Out[3]: array([  10,1000])

In [4]: np.power(x,2)
Out[4]: array([    100,10000,1000000])

In [5]: y = np.array([1,2,3])

In [6]: y
Out[6]: array([1,3])

In [7]: np.power(x,y)
Out[7]: array([        10,1000000000])

numpy.mod() 函数

计算输入数组中相应元素的相除后的余数，函数 numpy.remainder() 也产生相同的结果

In [1]: import numpy as np

In [2]: x = np.array([10,20,30])

In [3]: x
Out[3]: array([10,30])

In [4]: y = np.array([3,5,7])

In [5]: y
Out[5]: array([3,7])

In [6]: np.mod(x,y)
Out[6]: array([1,2])

In [7]: np.remainder(x,y)
Out[7]: array([1,2])