CVX cannot solve:

maximize (X1*inv_pos(1+X2))

s.t. convex constraints <= 0

where X1 and X2 are positive variables.

With Hessian Matrix, we find that X1*inv_pos(1+X2) is joint concave with regarding to Y1 and Y2.

Below are the error messages in Matlab:

Error .* (line 173)

Disciplined convex programming error:

Cannot perform the operation: {real affine} .* {convex}Error * (line 36)

z = feval( oper, x, y );Error ObjFuc_aim (line 35)

maximize ( -Y1*inv_pos(1+Y2));

Thanks ahead!!!