[Python] 分段線性插值

利用線性函數做插值

每一段的線性函數：

#Program 0.6 Linear Interploation
import numpy as np
import matplotlib.pyplot as plt

#分段線性插值閉包
def get_line(xn, yn):
    def line(x):
        index = -1
        
        #找出x所在的區間
        for i in range(1, len(xn)):
            if x <= xn[i]:
                index = i-1
                break
            else:
                i += 1
        
        if index == -1:
            return -100
        
        #插值
        result = (x-xn[index+1])*yn[index]/float((xn[index]-xn[index+1])) + (x-xn[index])*yn[index+1]/float((xn[index+1]-xn[index]))
        
        return result
    return line

xn = [i for i in range(-50,50,10)]
yn = [i**2 for i in xn]

#分段線性插值函數
lin = get_line(xn, yn)

x = [i for i in range(-50, 40)]
y = [lin(i) for i in x]

#畫圖
plt.plot(xn, yn, 'ro')
plt.plot(x, y, 'b-')
plt.show()