为什么@file函数无法打开1_2.txt文件

model:
!6发点8收点运输问题;
sets:
warehouses/ @file('1_2.txt') /: capacity;
vendors/ @file('1_2.txt') /: demand;
links(warehouses,vendors): cost,volume;
endsets
!目标函数;
min=@sum(links: cost*volume);
!需求约束;
@for(vendors(J):
@sum(warehouses(I): volume(I,J))=demand(J));
!产量约束;
@for(warehouses(I):
@sum(vendors(J): volume(I,J))<=capacity(I));
!这里是数据;
data:
capacity = @file('1_2.txt') ;
demand = @file('1_2.txt') ;
cost = @file('1_2.txt') ;
enddata
end