求助各位高手们：这个循环该怎样写啊？

hehairen

xt=[162,175,162,156,174,157,154,177,159,171,166,162,171,183,163,152,165,175,167]’
  xt为一列向量，a为一行向量，
a=[0.1972,0.0793,-0.0041,0.0990,-0.0250,0.0262,-0.0022,0.0979,0.2454,-0.2224,0.3678,-0.1068,0.0990,0.2240,-0.0477,-0.0294] ,
y向量中的元素y(1),y(2),y(3),.......y(17)分别为：
y(1)=xt(1)
y(2)=a(1)*y(1)
y(3)=a(1)*y(2)+a(2)*y(1)
y(4)=a(1)*y(3)+a(2)*y(2)+a(3)*y(1)
y(5)=a(1)*y(4)+a(2)*y(3)+a(3)*y(2)+a(4)*y(1)
.......................
y(17)=a(1)*y(16)+a(2)*y(15)+.......+a(16)*y(1)
请高手们指点迷津啊

buaalqq

y(:)=0;
y(1)=xt(1);
for k=2:17
for n=1:k-1
y(k)=y(k)+a(n)*y(k-n);
end
end
试一下吧，就这个思路。
记不清要几个end了。

第一步是将y向量赋零。

[ 本帖最后由 ChaChing 于 2009-4-22 14:07 编辑 ]

hehairen

我按您的思路运行了一下，发现y(1)=xt(1),当k=2,n=1时y(2)=y(2)+a(1)*y(1).MATLAB提示等号右边的y(2)没有事先赋值........
还请您再解决一下啊

bainhome

1. function xunhuan
   
2. clc
   
3. xt=[162,175,162,156,174,157,154,177,159,171,166,162,171,183,163,152,165,175,167]';
   
4. a=[0.1972,0.0793,-0.0041,0.0990,-0.0250,0.0262,-0.0022,0.0979,0.2454,-0.2224,...
   
5.     0.3678,-0.1068,0.0990,0.2240,-0.0477,-0.0294];
   
6. xt1=xt([1:length(a)])';
   
7. y=xt(1);
   
8. for i=2:length(xt1)   
   
9.     y=[y,sum(a(1:i-1).*fliplr(y(1:i-1)))];
   
10. end

复制代码

[ 本帖最后由 bainhome 于 2006-8-5 15:00 编辑 ]

hehairen

我运行后得出y =
  Columns 1 through 7
  162.0000   31.9464   47.3566   45.1597   58.9303   59.2944   60.0264
  Columns 8 through 14
   57.7281   79.5181  116.5706   83.9168  138.7380  125.7661  143.4469
  Columns 15 through 16
  173.5141  177.0229
但手算后发现y1=xt(1)=162, y(2)=a(1)*y(1)=0.1972*162=31.9464,
y(3)=a(1)*y(2)+a(2)*y(1)=0.1972*31.9464+0.0793*162=19.14643,
发现y(3)与运行的结果不相等啊，还请帮忙啊

hehairen

谢谢前辈的指点啊！我以后一定努力动脑！

buaalqq

y(2)初值为零啊，y整个向量初值都为零啊。
你是不是没有把y向量初始化为零啊？