Hi Morteza,
As per my understanding of the question you want to plot a “Polyhedron” in a 2-dimensional plot using only two of its axes (“x1” and “x2” specifically)
I believe the “Polyhedron” you are using is from the MATLAB based MPT3 library and if not, you can use the following instructions to install it - https://www.mpt3.org/Main/Installation#:~:text=If%20you%20for%20any%20reason%20cannot%20use%20tbxmanager%2C,5%20Save%20your%20Matlab%20path%20for%20later%20use
As you have mentioned, it is not possible to plot a 4-dimensional figure. However, you can plot the projection of the 4-D figure on a 2-D plane by using only the x1 and x2 states.
Here’s the code to achieve that:
xmin = [-2; -5;-4; -2];
xmax = [0; 50; 10; 10];
X = Polyhedron('lb',xmin,'ub',xmax);
P = X.projection([1,2]);
P.plot()
Hope this answers your question!
