CVX error in using pow_cvx

Nonconvex
2

You have violated CVX’s rules for inv_pos` . Why isn't CVX accepting my model? READ THIS FIRST!

I am presuming Matrix(ii,kk) >= 0 due to being a singular value of something. Therefore, the argument of inv_pos is convex, which is not allowed (unless affine, which this is not).

help inv_pos

inv_pos Reciprocal of a positive quantity.
inv_pos(X) returns 1./X if X is positive, and +Inf otherwise.
X must be real.

 For matrices and N-D arrays, the function is applied to each element.

  Disciplined convex programming information:
      inv_pos is convex and nonincreasing; therefore, when used in CVX
      specifications, its argument must be concave (or affine).

Indeed, obj(ii,kk) is non-convex. Looking at the 2nd derivative of the RHS, even for Pa(ii,kk) > 0, the sign of the 2nd derivative changes from negative to positive at Pa(ii,kk) = 1/sqrt(Matrix(ii,kk)*a), assuming that Matrix(ii,kk) > 0 ;