Install CVXQUAD https://github.com/hfawzi/cvxquad . Then use its quantum_entr function. There is no need to install CVXQUAD’s exponential.m replacement.
Also see the discussion of matrix log related functions in CVXQUAD at the end of 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 and the reference https://arxiv.org/abs/1705.00812 .