关于一个循环求和的问题

shiyiming

sum t从2到100：[y(t)+y(t-1)+y(t-2)+.....+y(t-k+1)-5]**2  k是已知的，k=2

我想用两个循环来做来着，可是总是出错，我是这么编的
data a;
input x1-x100@@;
array x[100] x1-x100;
a=mean(of x1-x100);
k=2；
do t=2 to 100;
  do i=0 to k-1;
   b+y[t-i];     /*b表示括号内的y(t)+y(t-1)+y(t-2)+.....+y(t-k+1)*/
   end;
c+(b-a*2)**2;  /*c表示总的和*/
end;
cards;
......
问题在于 算的总是不对  跪求大家帮帮我.......

shiyiming

Hope the following is waht you want:

data a;
input x1-x5;
array x[5] x1-x5;
a=mean(of x1-x5);
k=2;
do t=2 to 5;
   do i=0 to k-1;
      b+x[t-i];
   end;
c+(b-a)**2;
b=0;
end;
drop t i;
cards;
1 1 1 1 1
2 2 2 2 2
3 3 3 3 3
;
run;

/* set b=0 after inner loop, or b value will be cumulated in each loop */