Describe the code and graph?

import numpy as np import matplotlib.pyplot as plt import scipy.integrate as sci from scipy.integrate import odeint def f(y,t): y1 , y2, y3 = y k1=1 k2=2 f = [-k1*y1,k1*y1-k2*y2,-k2*y2] return f #initial conditions f_initial=[3,3,3] t = np.linspace(0,20,1000) solvenumarica= sci.odeint(f,f_initial,t) plt.plot(t,solvenumarica[:,2],'-',label='y1 (parent)') plt.plot(t,solvenumarica[:,1],'-',label='y2 (daughter)') plt.plot(t,solvenumarica[:,2],'-',label='y3 (granddaughter)') plt.title('Nuclear_decay') plt.ylabel('Activity (n)') plt.xlabel('time (t)') plt.legend() plt.grid(True) plt.show()