How to write a equation that x*(2^(y/x)-1) in CVX

2

x*(2^(y/x)-1) = x*exp(y*log(2)/x) - x

x*exp(y*log(2)/x can be replaced by a variable z and the constraint
{y*log(2),x,z} == exponential(1)

So the variable z is declared, x*(2^(y/x)-1) is replaced by z-x, and the constraint {y*log(2),x,z} == exponential(1) is added.