python实现matlab中的filter函数

matlab中的filter函数：

y = filter(b,a,x)

python实现matlab中的filter函数

def filter_matlab(b,a,x):
    y = []
    y.append(b[0] * x[0])
    for i in range(1,len(x)):
        y.append(0)
        for j in range(len(b)):
            if i >= j :
                y[i] = y[i] + b[j] * x[i - j ]
                j += 1
        for l in range(len(b)-1 ):
            if i >l:
                y[i] = (y[i] - a[l+1] * y[i -l-1])
                l += 1
        i += 1
    return y

example:

取

b =  [8,-3.5,0.5]

a =  [1,-1.5,0.25]

x = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]

y = filter_matlab(b,a,x)

函数的结果和matlab的filter函数结果一致，为

[8,
 24.5,
 52.25,
 94.75,
 156.5625,
 243.65625,
 363.84375,
 527.3515625,
 747.56640625,
 1042.01171875,
 1433.6259765625,
 1952.43603515625,
 2637.74755859375,
 3541.0123291015625,
 4729.581604003906,
 6291.619323730469,
 8342.533584594727,
 11033.395545959473,
 14561.959922790527,
 19187.090997695923]