@sand15 Since finding maximum (or minimum) on 3D functions can be sometrime tricky. For example f(x,y)=sin(x)*cos(x). I think that the user could have to give the point and the planes that he want. 

Byt the way, see what the new software ExaktAI from our friend Edgardo can do when I used it with maple as computing engine and save it as maple document.:

plot3d(sin(x)*cos(y), x = -10 .. 10, y = -10 .. 10)

We see the grid and as the mouse move, we wee lines that shows the plane, if I underestand correctly the result. It is nice. It was save as a maple document. But when I opened it in Maple 2026, the magic was gone. Too bad. It should be a plot,options

Thank you for taking the time to answer me.

@Carl Love Thank you for taking the time to answer me.

@C_R Thank you for taking the time to answer me. I love the use of zgradient. I will use that command more:

colorscheme = ["zgradient", ["blue", green, "yellow", "red"], zrange = 0 .. 1]

But I do want the effect Matlab style.

@nm Thank you for taking the time to mention the Physics package. In this instance, I did not want to go there. But when I need to use them in QFT, that is the way I go.

@acer Thank you for your worksheet.

@dharr Thank you very much for your answer. Why did I not think about that one? Anyway, your code work fine and I was able to defined all the others one. Mario

@dharr It is true that sometimes, I do have the problem of a formula that becomes numbers when I want the equation. Then I have to go tho the palettes "Variable" to unassigned it. Your comments sound right to me. So I will use eval as acer talked about it. You have convinced me to the advantage of using it. Thank you for making me rethink this.

@acer Thank you acer for this tip too. I can always count on you. Maybe I could send you my question directly to you :-)

I know, the others deserve to learn too!

@acer Thank you for your help. I love this solution:

that make me learn a new trick in Maple. Then I do the because I am too lazy to write "eval" all the time.

Thank again acer!

@dharr Thank you for taking the time to help me solve this.

@Kitonum  Thank you!

@dharr Thank you for the command from plots. I also tried this:

>FunctionAdvisor(plot, Zeta)

which give you the plot from FunctionAdvisor without loading anything. But the inability to exract the command in a cell is bizarre. The closest I come is by doing this:

>plots_Zeta := MathematicalFunctions:-Get(plot, Zeta)

>plots_Zeta[2][1]

Which give the plot I was looking for. But again, cannot ge the commands. If I could send this plot to the PlotBuilder, I could see those commands.

But at least, you help me discover a new world to explore. Thank you.

@Scot Gould That is what I would do because the Mac environment is unknown to me. Happy to know that it serve to someone.

@Scot Gould

In the video, it is very clearly said to create the "Users" directory. I simply missed that because I was opening the maple initialization help page while listening to the video. My mistake, of course.

Thank you for your help Scot

@acer You are making me regret to have moved from Ubuntu to Windows.

But I don't have any "maple.ini" file elsewhere. What I noticed is that the file's name is "Maple.ini," with a capital M. Which is the preferences file as you duly noted.

Do you think that this means that I should create a blank "maple.ini" file, write the three setoptions lines and save it at this location: C:\Program Files\Maple 2024\lib\maple.ini ?

Because there is no "maqple.ini" file in the \lib folder neither.

Thank you acer for your help.