Multiple_NR.py

#Last update:Piyush
import numpy as np 
import matplotlib.pyplot as plt
import random

x=np.linspace(-5,10,200)
def f(x):     #function
  return x**3-3*x+1
def f_prime(x):   #first derivative
  return 3*x**2-3

def newtoroot(f, df, x0, tol):  #newton raphson method
    if abs(f(x0)) < tol:
        return x0
    else:
        #print(x0)
        return newtoroot(f, df, x0 - f(x0)/df(x0), tol)
start = []
num   = 10
N     = 5
for i in range(num):
  c=random.randrange(-N, N)
  if(f_prime(c)>0):
    start.append(c)
print(start)

result=[]
for i in range(len(start)):
  result = newtoroot(f,f_prime,start[i], 1e-5) #broo nikal root nikaal
  print("root =", result)
plt.figure(figsize=(6,4));plt.xlim([-5,5]);plt.ylim([-5,10])
plt.plot(x,f(x),label=r'$f(x)$',linewidth=2.0,color='deeppink')
plt.axvline(x=result,color='black',linewidth=1.3);
plt.axhline(y=0,color='grey')
plt.legend(fontsize='12')