Supercritical fluid chromatography is an experimental technique for analyzing compositions of mixtures. It utilizes a carrier fluid, often carbon dioxide, in the dense fluid region just above the critical temperature. Write a program to express the fluid density as a function of reduced temperature and pressure in the region of 1.0 ≤ T_r ≤ 1.2 in reduced temperature and 2 ≤ P_r ≤ 8 in reduced pressure. The relation should be an expression curve-fitted to values consistent with the generalized compressibility charts.