Disciplined convex programming information:
norm is convex, except when P<1, so an error will result if
these non-convex "norms" are used within CVX expressions. norm
is nonmonotonic, so its input must be affine.
norm (with P >= 1) of an affine function is convex, and therefore can be used in a constraint
norm( ) <= affine expression
where affine expression can be a constant. Equality constraints on norms are non-convex (except for trivial cases, such as right-hand side = 0) and are not allowed in CVX.
I don't know what exactly you're doing with
trace(Z) == 1 , but if trace(Z) is not an affine function of the CVX (optimization) variables, it is non-convex and will be rejected by CVX.