title: FOURTH DERIVATIVE - My graph is wrong, please let me know my mistake
body: <p>For the fourth derivative, this is my code:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  
  pi=np.pi
  x=np.arange(0,5*pi,0.03*pi)
  y=np.cos(x)
  
  h=x[4]-x[3]
  
  "fourth derivative"
  
  #first formula
  
  der41=[]
  x41=[]
  
  for i in range(2,len(y)-2,1):
      der41.append((y[i+2]-4*y[i+1]+6*y[i]-4*y[i-1]+y[i-2])/(h**4))
      x41.append(x[i])
  
  der41=np.array(der41)
  x41=np.array(x41)
  
  #Second formula
  
  der42=[]
  x42=[]
  
  for i in range(3,len(y)-3,1):
      der42.append((-y[i+3]+12*y[i+2]+39*y[i+1]+56*y[i]-39*y[i-1]+12*y[i-2]+y[i-3])/(6*h**4))
      x42.append(x[i])
  
  der42=np.array(der42)
  x42=np.array(x42)
  
  plt.plot(x,y,'g',x41,der41,'r',x42,der42,'b')
  plt.title("Cuarta derivada")
  plt.xlabel("Eje X")
  plt.ylabel("Eje Y")
  plt.grid()
  plt.show()
  </code></pre>
  
  <p>This is the graph:</p>
  
  <p><a href="https://i.stack.imgur.com/2enmM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2enmM.png" alt="enter image description here"></a></p>
  
  <p>This code is based on the following formulas:</p>
  
  <p><a href="https://i.stack.imgur.com/ktjoQ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ktjoQ.png" alt="enter image description here"></a></p>
  
  <p>All three graphs should be the same "shape". </p>
  
  <p>PD: Sorry if i have mistaken a word, please let me know. Thank you.</p>