Atomic, Molecular and Optical Physics | Condensed Matter Physics | Physical Chemistry
The van der Waals (from his thesis of 1873) equation is a cubic in the molar volume. Plotting the equation in pseudo 3 dimensions is quite simple to do, but including tie lines is quite difficult. Employing the solutions to the cubic van der Waals equation, the tie lines are readily available and can be easily incorporated into the aforementioned 3D plots.
David, Carl W., "Plotting the van der Waals Fluid in pseudo-3D and the Maxwell Construction" (2015). Chemistry Education Materials. 89.