Hello, I have run into the error “Invalid quadratic form(s): not a square.” Here is my code:

```
1.cvx_begin quiet
2. variable x
3. variable y
4. minimize (x^2+y^2-3*x*y)
5. subject to
6. x+y==1
7.cvx_end
8. for i=1:10
9. cvx_begin quiet
10. variable x1
11. variable y1
12. minimize (x1^2+y1^2-3*x*y-(grad([x;y])'*[x1;y1]+1/2*norm([x1;y1]*[x;y],2)^2))
13. subject to
14. x1+y1==1
15. cvx_end
16. x=x1;
17. y=y1;
18. end
19. fprintf('R=%.4f\n',cvx_optival)
20. fprintf('x=%.4f\n',x)
21. fprintf('y=%.4f\n',y)
```

error:

```
>> SCA_eg
Error using times>times_q (line 84)
Disciplined convex programming error:
Invalid quadratic form(s): not a square.
Error in cvx_binary_op (line 107)
Error in .* (line 53)
Error in * (line 35)
Error in SCA_eg (line 4)
minimize (x^2+y^2-3*x*y)
```

I would greatly appreciate your assistance in resolving this error.