How to express this expression

Hi, everyone! The variable and objective function are as follows,how to express the objective in CVX?
Thank you for your time!

variable: v(1,N)
objective: minimize ( ||v[N+1]||^2 - ||v[1]||^2)

It is impossible by dimension.

Thank you for your reply !
the dimension of v is declared as N , hence v[N+1] is impossible.
Thank you very much!

But if the dimension of v is N+1, how can I express the objective function: min ||v[N+1]||^2- ||v[1]||^2 ?

It is not convex.

I get it, thank you!