python - 为什么包络线一开始是错误的？

我实现了一个给出离散值包络曲线的函数。我认为可能会出现错误，因为当我在帖子的底部为您提供一个日期进行测试时，我得到了真实数据点和包络线曲线之间的差异，如图所示

from scipy.interpolate import interp1d
import numpy as np
import matplotlib.pyplot as plt

def enveloppe(s):
    u_x = [0,]
    u_y = [s[0],]
    q_u = np.zeros(s.shape)
    for k in xrange(1,len(s)-1):
        if (np.sign(s[k]-s[k-1])==1) and (np.sign(s[k]-s[k+1])==1):
            u_x.append(k)
            u_y.append(s[k])
    u_x.append(len(s)-1)
    u_y.append(s[-1])
    u_p = interp1d(u_x,u_y, kind = 'cubic',bounds_error = False, fill_value=0.0)
    #Evaluate each model over the domain of (s)
    for k in xrange(0,len(s)):
        q_u[k] = u_p(k)
    return q_u

fig, ax = plt.subplots()
ax.plot(S, '-o', label = 'magnitude')
ax.plot(envelope(S), '-o', label = 'enveloppe magnitude')
ax.legend()

Data S : array([  9.12348621e-11,   6.69568658e-10,   6.55973768e-09,
         1.26822485e-06,   4.50553316e-09,   5.06526113e-07,
         2.96728433e-09,   2.36088205e-07,   1.90802318e-09,
         1.15867354e-07,   1.18504790e-09,   5.72888034e-08,
         6.98672478e-10,   2.75361324e-08,   3.82391643e-10,
         1.25393143e-08,   1.96697343e-10,   5.96979943e-09,
         1.27009013e-10,   4.46365555e-09,   1.31769958e-10,
         4.42024233e-09,   1.42514400e-10,   4.17757107e-09,
         1.41640360e-10,   3.65170558e-09,   1.29784598e-10,
         2.99790514e-09,   1.11732461e-10])

最佳答案

我将对您的信封功能进行两次修改，以获得更单调的输出



这样做的目的是避免将左端和右端隐式添加到用于构建包络的峰列表中

def enveloppe(s):
    u_x = [] # do not add 0
    u_y = []
    q_u = np.zeros(s.shape)
    for k in range(1,len(s)-1):
        if (np.sign(s[k]-s[k-1])==1) and (np.sign(s[k]-s[k+1])==1):
            u_x.append(k)
            u_y.append(s[k])
    print(u_x)
    u_p = interp1d(u_x,u_y, kind = 'cubic',
              bounds_error = False,
              fill_value="extrapolate") # use fill_value="extrapolate"
    for k in range(0,len(s)):
        q_u[k] = u_p(k)
    return q_u

关于python - 为什么包络线一开始是错误的？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/45569589/