Lane-Emden Equation in Stellar Structure
The Lane–Emden equation is , where dimensionless variables and relate to the density and radius (see Details). The equation is used in the study of polytropic gaseous spheres and the modeling of stars. Solutions of this second-order differential equation use polytropes to relate pressure and density as a function of , the radial coordinate measured from the center of the polytropic sphere (the star); and have the polytropic relation , where is the polytropic constant and is the polytropic index that you can choose with the control.
Typically we are interested in finite solutions at . If we take the values and to be the densities, then .
The relationship between the radial coordinate and its dimensionless counterpart is
where is the gravitational constant. The relationship between the density and its dimensionless counterpart is .
Studies and derivations of these relations and the Lane–Emden equation can be found in  and .
 S. Chandrasekhar, An Introduction to the Study of Stellar Structure, Chicago: University of Chicago Press, 1939.
 R. Kippenhahn and A. Weigert, Stellar Structure and Evolution, Berlin: Springer-Verlag, 1994.