import numpy as np
import matplotlib.pyplot as plt

n=120.0
h=.1
y=np.zeros(int(n+1))
z=np.zeros(int(n+1))
y[0]=1.5
z[0]=1.5

for i in range(int(n)):
    y[i+1]=y[i]+h*y[i]*(2-z[i])
    z[i+1]=z[i]+h*z[i]*(y[i+1]-1)

# jeg har aldri faatt plt.show() til aa funke, saa vi lagrer figuren i en fil som heter 'hei'
plt.plot(y,z)
plt.savefig('hei')