import matplotlib.pyplot as plt
import numpy as np

def heaviside(x):
    return np.heaviside(x, 1)
def E(t, v, d, T):
    sum_term = np.sum(d*np.heaviside(t - T,1))
    return v * t - sum_term

v = 1.0 #[mm/year]
T = np.array([10,20,40])
d = np.array([3,8,5])

N = 500
Tmax = 50
dt = Tmax/N

t = np.zeros(N)
y = np.zeros(N)

for i in range(N):
    t[i] = i*dt
    y[i] = E(t[i], v, d, T)

plt.plot(t, y)
plt.show()