Numpy 基础

1. 数组

1.1 数学操作

# -*- coding: utf-8 -*-
import numpy as np
a = [1, 2, 3, 4]  # a为列表，若此时执行 a + 1 将报错
a = np.array(a)
a  # array([1, 2, 3, 4])
a + 1   # array([2, 3, 4, 5])
b = array([2, 3, 4, 5])
a + b  # array([3, 5, 7, 9])
a * b  # array([2, 6, 12, 20])
a ** b  # array([1, 8, 81, 1024])

1.2 提取数组中的元素

a[0]  # 1
a[:2]  # array([1, 2])  # 提取前两个元素
a[-2:]  # array([3, 4])  #提取最后两个元素

1.3 修改数组形状，多维数组

a.shape  # (4L,) 查看array形状
a.shape = 2,2  # 修改array形状
a  # array([[1, 2], [3, 4]])
a * a  # array([[1, 4], [9, 16]]) 对应元素乘积

1.4 画图

a = linspace(0, 2*pi, 21)
a
>>array([ 0.   ,  0.314,  0.628,  0.942,  1.257,  1.571,  1.885,  2.199,
        2.513,  2.827,  3.142,  3.456,  3.77 ,  4.084,  4.398,  4.712,
        5.027,  5.341,  5.655,  5.969,  6.283])
b = sin(a)
b
>>array([  0.000e+00,   3.090e-01,   5.878e-01,   8.090e-01,   9.511e-01,
         1.000e+00,   9.511e-01,   8.090e-01,   5.878e-01,   3.090e-01,
         1.225e-16,  -3.090e-01,  -5.878e-01,  -8.090e-01,  -9.511e-01,
        -1.000e+00,  -9.511e-01,  -8.090e-01,  -5.878e-01,  -3.090e-01,
        -2.449e-16])