 # Illogical change of output

Hello, I wrote this code to visualize the solution of a differential equation, but I observed that a change happens in the the ordinate’s amplitude in the abscissa 0 if I increased the length of the abscissa from 200 to 400
Please, Is what happened a problem? If yes, how can I fix it?
CODE :
from numpy import *
from matplotlib.pyplot import *
from scipy.integrate import odeint
k = 28410**5
w0 = 512.8
F0 = 131
𝝃 = 0.05
m = 108
c = 2
𝝃w0m
β = 0.1
w = 0.01
def F(Y,t) :
Zzero, Zun = Y, Y
return array([ Zun, (1/m)(-kZzero-cZun+F0cos(wt)-βZzero**3)])
vi = [0, 0]
t1 = linspace(0 ,200, 100000)
t2 = linspace(0 ,400, 100000)
solution1 = odeint(F, vi, t1)
solution2 = odeint(F, vi, t2)
Z01 = solution1 [ :, 0]
Z02 = solution2 [ :, 0]
subplot(211)
plot(t1, Z01, label = “Cote”)
legend()
xlabel(" Temps (s)")
ylabel(“Déplacement1 (m)”)
grid(True)
rcParams[‘figure.figsize’] = [15, 8]
subplot(212)
plot(t2, Z02, label = “Cote”)
legend()
xlabel(" Temps (s)")
ylabel(“Déplacement2 (m)”)
grid(True)
rcParams[‘figure.figsize’] = [15, 8]
show()

Thank you and good day.