How can i solve the problem

here is a simple case ,but cvx says i cant use a variable as denominater.i think i violate the DCP ruleset, but i dont know how to fix it, can anybody help me

variables a
subject to

the errors are :
Disciplined convex programming error:
Cannot perform the operation: {positive constant} ./ {real affine}

出错 ./ (line 19)
z = times( x, y, ‘./’ );

出错 * (line 36)
z = feval( oper, x, y );

出错 / (line 15)
z = mtimes( x, y, ‘rdivide’ );

出错 Untitled2 (line 4)

My original reply here was erroneous, because I misread the post.

but a is out of the log would be clearer to rewrite log(1+1/a)a as alog(1+1/a). so i think log(1+1/a)*a can’t be rewritten as log(a+1).

Sorry, I misread the post.

Reformulate as

ok,i will try it. Thank you very much!

Unfortunately, that is concave, so it can be maximized, but not minimized in CVX.

thank you a lot! i got this one, but i have a more complex problem to’s kind similar to this simple problem. How can i solve this problem