求教用c语言实现IIR巴特沃斯低通滤波器效果

实验数据：

x=[-0.0289, 0.3943, 0.9965, 1.1266, 0.9995, 1.0891, 1.2262, 1.0699,...

0.8990, 0.7685, 0.7844, 0.9471, 1.4317, 1.6765, 1.7629,-3.2903,...

3.4122, 4.5403,-2.1667,-2.0584, 4.6694, 2.0368,-0.4864, 0.1427,...

2.5652,-1.8980,-0.0527,-1.4730, 2.7884,-6.4092, 2.9084,-5.1428,...

1.5929, 0.0014,-0.6010,-4.3059,-0.4518, 1.9959,-3.3526, 0.5745,...

-3.5487, 0.5913,-0.2472,-1.5479,-2.4422, 2.5066,-4.2421,-2.3588,...

3.8869,-3.9855, 0.9583,-1.2164, 3.7050, 1.2411,-1.7249, 0.9964,...

3.9695, 1.3400,-3.5513, 5.8552,-2.8092, 2.6877, 0.4444, 3.5641,...

-2.3496, 3.6065,-1.7598, 1.4699, 3.7201,-1.1626, 2.5171,-1.8247,...

2.5076, 2.5423,-0.1164, 0.3413,-2.8366,-0.5732, 1.1705,-1.1689,...

-1.8778,-2.8823, 0.1312, 0.1701,-0.3147,-3.2178,-0.2897,-0.2661,...

-2.6156, 2.5836,-6.1123, 0.3611, 3.8320,-5.1405,-2.4962, 1.3115,...

0.3410,-5.0227, 2.5150,-2.2485, 0.8696,-0.4257,-0.2326, 5.2529,...

-1.1389,-1.0966, 4.2358,-0.8846, 1.3454, 2.1462,-0.2605, 1.8075,...

-1.5669, 3.4374, 2.4737,-0.9521, 1.0952, 0.2180, 0.3156, 4.8910,...

-1.5372, 1.4585,-1.0904, 5.1795,-1.9366,-1.0818, 1.2667,-0.4268];

用matlab设计出低通数字巴特沃斯滤波器的系统函数，分子 分母系数为

B =

0.0118    0.0473    0.0709    0.0473    0.0118

A =

1.0000   -1.8778    1.6214   -0.6630    0.1087

然后转化为差分方程y[n]=(0.0118+0.0473*x[n-1]+0.0709*x[n-2]+0.0473*x[n-1]+0.0118*x[n-4])/(1.0000-1.8778*y[n-1]+1.6214*y[n-2]-0.6630*y[n-3]+0.1087*y[n-4]);

x[n]序列已知，怎么确定初始条件y[0],y[1],y[3]的值呢？我用0代替后发现结果与matlab里面算得的输出值不一样，求教高手帮忙指点下啊？matlab里面输出值为：

y =

Columns 1 through 10

-0.0003    0.0027    0.0339    0.1462    0.3755    0.6820    0.9672    1.1520    1.2180    1.1849

Columns 11 through 20

1.0834    0.9537    0.8519    0.8438    0.9738    1.1639    1.1797    0.9669    0.8653    1.0306

Columns 21 through 30

1.1044    0.9217    0.8283    1.0009    1.1817    1.1554    0.9198    0.4972   -0.0200   -0.4327

Columns 31 through 40

-0.6916   -0.9279   -1.1940   -1.3770   -1.2927   -0.9504   -0.7048   -0.8215   -1.0777   -1.1383

Columns 41 through 50

-1.0217   -0.9535   -1.0106   -1.0546   -0.9966   -0.9284   -0.8979   -0.9115   -1.0399   -1.1710

Columns 51 through 60

-1.0828   -0.8209   -0.5377   -0.1675    0.3855    0.9074    1.1003    1.0762    1.1264    1.1970

Columns 61 through 70

1.1175    0.9498    0.8109    0.7839    0.9316    1.1502    1.2378    1.1130    0.8760    0.7619

Columns 71 through 80

0.9013    1.1253    1.1727    1.0169    0.8966    0.9660    1.0313    0.7622    0.1025   -0.5938

Columns 81 through 90

-0.9430   -0.9802   -1.0259   -1.1968   -1.2764   -1.0988   -0.8442   -0.7780   -0.9019   -1.0364

Columns 91 through 100

-1.0595   -1.0511   -1.1250   -1.1107   -0.8994   -0.8015   -0.9698   -1.1263   -1.1274   -1.0791

Columns 101 through 110

-0.9910   -0.8003   -0.5268   -0.1960    0.2717    0.8555    1.2564    1.2939    1.1396    0.9958

Columns 111 through 120

0.9457    0.9907    1.0294    0.9534    0.8384    0.9003    1.1390    1.2758    1.1309    0.8411

Columns 121 through 128

0.7268    0.9213    1.1684    1.1892    1.0659    0.9769    0.8262    0.4928