You need to express that as a quadratic forum. If you do that, or just calculate the Hessian of x1^2+y1^2-4*x*y, you will see that the Hessian is indefinite, so that the expression is neither convex nor concave. Therefore it can’t be used in CVX.
You need to express that as a quadratic forum. If you do that, or just calculate the Hessian of x1^2+y1^2-4*x*y, you will see that the Hessian is indefinite, so that the expression is neither convex nor concave. Therefore it can’t be used in CVX.