Please help me to fix the problem

cvx_begin gp
variables X y
variables z(10)
minimize(X^2-X*z(2)*log(y))
2<=z<9
10>= X >= 1
7<=y<=20
cvx_end
X
y
z

Disciplined convex programming error:
Cannot perform the operation: {log-affine} .* {real affine}

This is non-convex. Why isn't CVX accepting my model? READ THIS FIRST!