I have a problem such as

minimize sum(S) - a * log2( 1 + S(1) / (S(2)+S(3)+N) ) - b * log2( 1 + S(2) / (S(1)+S(3)+N) ) - c * log2( 1 + S(3) / (S(1)+S(2)+N) )

where S is the variables to be optimized,

This problem is convex to S, how can I express this problem in CVX?

The problem description just now is not clear, sorry~

Thanks very much for your answer~