If you are getting this message, then change the function or variable name so that they don;t conflict. Do you have some other question?
Given your use of exp, I suggest you use CVXQUAD in order to improve reliability and performance. Please read CVXQUAD: How to use CVXQUAD's Pade Approximant instead of CVX's unreliable Successive Approximation for GP mode, log, exp, entr, rel_entr, kl_div, log_det, det_rootn, exponential cone. CVXQUAD's Quantum (Matrix) Entropy & Matrix Log related functions