后向算法

A = [[0.5, 0.2, 0.3],
     [0.3, 0.5, 0.2],
     [0.2, 0.3, 0.5]]

B = [[0.5, 0.5],
     [0.4, 0.6],
     [0.7, 0.3]]

pi = [0.2, 0.4, 0.4]

a1 = [1, 1, 1]

t = [0,0,1]


def q(a1,t):
    result = []
    for i in range(len(pi)):
        c = 0
        for j in range(len(pi)):
            c += A[i][j] * B[j][t] * a1[j]
            print(A[i][j], B[j][t], a1[j], c)
        print('-'*50)
        result.append(c)
    return result


a1 = q(a1, 0)
a1 = q(a1, 1)