It is easy to see 1/(1 +exp(x)) is convex when x > 0. However, the following code doesn’t work. Is there a better to rewrite the problem?

```
cvx_begin
variable x(n) nonnegative
minimize( sum(inv_pos(1 + exp(x))) )
subject to
sum(inv_pos(2-x)) <= R
x >= 1
x < 2
cvx_end
```