import numpy as np

a = np.array([[1,9],[2,9],[3,9],[4,9],[5,9],[6,9],[7,9],[8,9]])
b = np.array([[]])
print(a)

for i in range(len(a)):
	if i > 0 and i % 2 == 0:
		b = np.append(b, a[i, 0] - a[i-2, 0])
	else:
		b = np.append(b, 0)

print(b.shape)

b = b.reshape(b.shape[0], 1)

print(b)

c = np.concatenate((a,b), axis=1)

print(c)