***利用scat3绘画看看***如果楼主还是坚持三维
webuse pennxrate
g lnppp=ln(ppp)
kdensity lnppp, nogr g(x s)
forv i=1970(10)2000{
kdensity lnppp if year==`i', nogr g(s`i') at(x)
la var s`i' "`i'Year"
loc m `m' s`i'
}
*line `m' x, sort ytitle(Density)
g g=1970 in 1/50
replace g=1980 in 51/100
replace g=1990 in 101/150
replace g=2000 in 151/200
forv a=1/150{
replace x=x[`a'] in `=50+`a''
}
forv b=1/50{
replace s1970=s1980[`b'] in `=50+`b''
replace s1970=s1990[`b'] in `=100+`b''
replace s1970=s1990[`b'] in `=150+`b''
}
g ss=s1970
scat3 x g ss
*g是时间,图形很难看,没办法啦,kdensity的default是50点
*如果您可以改成1000点,就会很漂亮的图。