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]
