I'm a PhD student in Economics and I would be very grateful if you could help me with this problem:
I got a function of three variables f(x,y,z). I want to get a 3d plot of the region A in R^3 such that for any vector of values (x,y,z) in A the function f is positive. I'm only able to solve this problem in a basic way: I fix one of the three variables -let's say z=Z -and then I get the 3d plot of the function f(x,y| z=Z), get the contour plot and define the region of interest. I can do it for several values of Z, but i think it is not very elegant.
There is a way to obtain the 3d plot of the variables space such that the condition of f being positive is satisfied?
Also, I have another question, which however is less crucial for me. Is there a way to plot in 3d two different functions in the same box?