请教如何用stata画出密度差异图

我也想知道这个分布密度差异曲线，正在做这方面

DESCRIPTION/AUTHOR(S)
      
       mkdensity produces kernel density estimates of several variables
      and graphs the result. As a default, it plots the densities of
      the given variables in one graph plot. It is also possible to
      handle panel data type structures using the over() and/or the
      by() options. mkdensity uses the kdensity command to calculate
      the underlying densities.
      
      KW: kernel density
      KW: density estimation
      KW: graphics
      
      Requires: Stata version 8
      
      Distribution-Date: 20160823
      
      Author: Szabolcs Lorincz, European Commission
      Support: email szabolcs@gmail.com
      

INSTALLATION FILES                                  (click here to install)
      mkdensity.ado
      mkdensity.sthlp