matlab 0—1规划问题提问

这是教员布置的一个练习题

我建立的数学规划模型是这样的

我写的求解过程如下：
clc,clear
a=load('data.txt');
c=a(1:end-1,1:end-1);
s=a(end,1:end-1);d=a(1:end-1,end);
prob=optimproblem;
x=optimvar('x',15,8,'Type','integer','LowerBound',0);
y=optimvar('y',15,8,'Type','integer','LowerBound',0,'UpperBound',1);
prob.Objective=sum(sum(c.*x));
prob.Constraints.con1=sum(x,1)<=s;
prob.Constraints.con2=sum(x,2)==d;
prob.Constraints.con3=sum(y,1)>=1;
prob.Constraints.con4=x>=1000;
prob.Constraints.con5=x<=2000;
[sol,fval,flag]=solve(prob);xx=sol.x;
writematrix(xx,'answer_practicce2_2.xlsx');
answer=fval

但是
为什么会像这个样子呀！