cvx_begin
variable x1
variable x2
variable x3
maximize -log(0.5*exp(-0.5*x1)+0.9*exp(-0.9*x2))
%maximize (1-exp(-0.5*x1)+1-exp(-0.9*x2)+1-exp(-1.2*x3))
subject to
x1 + x2 + x3 <= 10
cvx_end

obj = 1-exp(-0.5*x1)+1-exp(-0.9*x2)+1-exp(-1.2*x3)
sprintf('Obj.= %3.3f',obj)
sprintf('x1 = %3.3f  x2= %3.3f x3= %3.3f',x1,x2,x3)
x1 = -10:.2:10
x2 = -10:0.2:10
[x1,x2] = meshgrid(x1,x2)
obj = 1-exp(-0.5*x1)+1-exp(-0.9*x2)+1-exp(-1.2*x3)
surf(x1,x2,obj)