import matplotlib.pyplot as plt
import numpy as np

x1 = np.linspace(-1,0)
x2 = np.linspace(0,1)
y1 = -x1
y2 = 2*x2

plt.figure(figsize=(8,3))
plt.plot(x1,y1,'r:',lw=3,label='y=-x')
plt.plot(x2,y2,'b-',lw=3,label='y=2x')
plt.plot([0],[0],'o',color='orange',markersize=10,label='Optimal')
plt.grid(); plt.legend()
plt.savefig('conditional.png',dpi=600)
plt.show()