Replace
log(cvx_expression)
with
-rel_entr(1,cvx_expresion)
But that won’t do you any good unless you install CVXQUAD and its exponential.m replacement, following the directions in 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