How to express three-dimensional variables in cvx?

I understand the solution of two-dimensional variables, but I need to solve the optimization of three-dimensional variables recently. Is this expression ok? MATLAB reports an error saying that the array exceeds the preset maximum array size. Maybe how should I do it.

Yes, CVX allow variables like that. But, how big are your N*I*k? Is it the line you posted that throws this error? If it’s not, can you provide more information on that?

Thank you for your reply。
Yes, MATLAB’s error line prompt is on this line, he says: The requested 3200000000x1 (23.8GB) array exceeds the preset maximum array size. Creating arrays larger than this limit can take a long time and cause MATLAB to become unresponsive.
I tried changing the size of N, I, K, no matter how small it will exceed

Why?Can you provide an error-reproducible code?