phasePlot8.py

import numpy as np
import matplotlib.pyplot as plt
import math
from scipy.integrate import odeint

M=19
m=1
g=9.81

def Atwood(y,t,M,m,g):
    
    #theta'(t)=omega(t)
    #radius'(t)=Rho(t)
    
    #omega'(t)=(1/radius(t))(-g*sin(theta(t))-2(Rho(t)*omega(t))
    #Rho'(t)=(1/(M+m))(m*radius(t)*(omega(t)^2)-M*g+m*g*cos(theta(t)))
    
    theta, omega, radius, Rho = y
    
    #dydt = [omega, (1/radius)*(-g*(np.sin(theta))-2*(Rho*omega)),Rho, (1/(M+m))*(m*radius*(omega^2)-M*g+m*g*(np.cos(theta)))]
    dydt = [omega, (1/radius)*(-g*(np.sin(theta))-2*(Rho*omega)), Rho, (1/(M+m))*(m*radius*(omega**2)-M*g+m*g*(np.cos(theta)))]
    
    return dydt
                           
#y0=[theta, change in theta, radius, change in radius]
y0 = [np.pi/2,0 ,1 ,0]
#time points
t = np.linspace(0,100,1000000)
#Solving the ODE
sul = odeint(Atwood, y0, t, args=(M,m,g))


plt.plot(sul[:,0], sul[:,1], 'r')
plt.ylabel('Angular velocity (radians per second)')
plt.xlabel('Angular displacement (radians)')
plt.title('Fig 8 - Phase Plot')
plt.grid()
plt.show()