Dear Intan,

I guess that I would need more information, on what exactly the problem is. The figure in the attached pptx document does not help.

In Maximize or NMaximize tend to work in 3D example. Let's look at:

Plot3D[Cos[x^2 + y^2]*Exp[-0.3 (x^2 + y^2)], {x, -6, 6}, {y, -6, 6}, PlotRange -> All]

If you then simply use the Maximize function you get:

Maximize[{Cos[x^2 + y^2]*Exp[-0.3 (x^2 + y^2)] && -6 < x < 6 && -6 < y < 6}, {x, y}]
(*{1., {x -> -1.06836*10^-8, y -> -7.75192*10^-9}}*)

which says that the maximum value of 1 is reached at (numerically) {0,0}.

Cheers, Marco

Maximize worked for me for a different function (using t, Q as example variables with example ranges)-

Maximize[{ Function [ ], 0<t<200 && 0<Q<1000}, {Q,t}]

Hello Marco, I found your reply here really helpful for me. May I ask you a followup question? Is there any way to indicate in the diagram the level of x and y where the maximum is achieved, and also the maximum? Thanks! Best, Hyun Woong