import numpy as np
import matplotlib.pyplot as plt

R = 1.0
E0 = 1.0

r = np.linspace(0, 2.5*R, 500)

E = np.where(r <= R, E0 * r / R, E0 * (R**2) / (r**2))

# plot
plt.plot(r, E)
plt.xlabel("r")
plt.ylabel("E(r)")
plt.grid(True)

plt.savefig("5.png", dpi=300, bbox_inches="tight")
plt.show()