I just started using CVX, and when I try to run the following Program, it shows the error ‘not a square’ in the ’ 4 * A * C == -1’,but I can’t find the reason,could you give me a guide?

cvx_begin

variables A B C D E F

expression P(N)

for n=1:N

P(n)=A*(x(n)^2)+B*x(n) y(n)+C(y(n)^2)+D*x(n)+E*y(n)+F;

end

```
minimize( norm(P,2))
subject to
B == 0
4 * A * C == -1
(E / (- 2 * C ))< MinY
(D/(-2*A)) <= Xlr(i,2)
(D/(-2*A)) >= Xlr(i,1)
```

cvx_end

error

Disciplined convex programming error:

Invalid quadratic form(s): not a square.

出错 * (line 36)

z = feval( oper, x, y );

出错 OSCA (line 135)

4 * A * C == -1