lingo显示check for undefined indices and/or conditions in expression:4错误信息是啥意思!

题目

lingo显示check for undefined indices and/or conditions in expression:4错误信息是啥意思!
model:
sets:
wh/1..5/;
vd/1..4/;
LINK(wh,vd):c,x;
endsets
Data:
c=66.8,57.2,78,70,67.4
75.6,66,67.8,74.2,71
87,66.4,84.6,69.6,83.8
58.6,53,59.4,57.2,62.4;
enddata
min= @sum(link:c*x);
@for(wh(i):@sum(vd(j):x(i,j))

答案

model:
sets:
wh/1..5/;
vd/1..4/;
LINK(wh,vd):c,x;
endsets
Data:
c=66.8,57.2,78,70,67.4
75.6,66,67.8,74.2,71
87,66.4,84.6,69.6,83.8
58.6,53,59.4,57.2,62.4;
enddata
min= @sum(link:c*x);
@for(wh(i):@sum(vd(j):x(i,j))