program define dists4
    version 4.0

    preserve
    clear

    quietly {
      set obs 501
      gen x=.
      gen y=.}

*-----------------------------------------------------------------------

    gph open, saving(z.gph,replace)
    gph pen 1

    replace x=3*((_n-251)/250)
    replace y=.4*uniform()
    graph y x, xlab(-3,-2,-1,0,1,2,3) ylab(0,.1,.2,.3,.4) s(i)
    gphconv

    pdf_Z x y
    lines x y
    gph text 1000 16000 0 0 The Z Curve

    gph close

*----------------------------------------------------------------------

    gph open, saving(t4.gph,replace)
    gph pen 1

    graph y x, xlab(-3,-2,-1,0,1,2,3) ylab(0,.1,.2,.3,.4) s(i)
    gphconv

    gph pen 2
    pdf_Z x y
    lines x y

    gph pen 1
    pdf_t x y 3
    lines x y

    pdf_t x y 5
    lines x y

    pdf_t x y 10
    lines x y

    pdf_t x y 20
    lines x y

    gph text 1000 16000 0 0 Z curve and t curves for 3, 5, 10, and 20 df

    gph close

*--------------------------------------------------------------------

    gph open, saving(chisq4.gph,replace)
    gph pen 1

    replace x=70*((_n-1)/500)
    replace y=.1*uniform()
    graph y x,xlab(0,10,20,30,40,50,60,70) ylab(0,.025,.05,.075,.1) s(i)
    gphconv

    pdf_chi2 x y 10
    lines x y

    pdf_chi2 x y 20
    lines x y

    pdf_chi2 x y 30
    lines x y

    pdf_chi2 x y 40
    lines x y

    gph text 1000 16000 0 0 chi-square curves for 10, 20, 30, and 40 df

    gph close

*------------------------------------------------------------------------

    gph open, saving(f4.gph,replace)
    gph pen 1

    replace x=2*(_n)/501
    replace y=2*uniform()

    graph y x, xlab(0,.5,1,1.5,2) ylab(0,.5,1,1.5,2) s(i)
    gphconv

    pdf_f x y 20 20
    lines x y

    pdf_f x y 40 40
    lines x y

    pdf_f x y 60 60
    lines x y

    pdf_f x y 80 80
    lines x y

    gph text 1000 16000 0 0 F Curves for (20,20), (40,40), (60,60), (80,80) df

    gph close

*------------------------------------------------------------------------

    graph using z.gph t4.gph chisq4.gph f4.gph

*------------------------------------------------------------------------

    restore
exit
end