program define n01
    version 4.0

    preserve
    clear

    set obs 401
    gen x=4*((_n-201)/200)
    gen y=exp(-(x^2)/2)/sqrt(2*_pi)
    gen x1=.
    gen x2=.
    gen y1=.
    gen y2=.

    gph open

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

    gphconv

    gph text 500 16000 0 0 The Z Curve

    replace x1=1 in 1
    replace x2=1 in 1
    replace y1=0 in 1
    replace y2=y[251] in 1

    replace x1=0 in 2
    replace x2=0 in 2
    replace y1=0 in 2
    replace y2=y[201] in 2

    replace x1=-1 in 3
    replace x2=-1 in 3
    replace y1=0 in 3
    replace y2=y[151] in 3

    replace x1=-2 in 4
    replace x2=-2 in 4
    replace y1=0 in 4
    replace y2=y[101] in 4

    replace x1=2 in 5
    replace x2=2 in 5
    replace y1=0 in 5
    replace y2=y[301] in 5

    replace x1=-3 in 6
    replace x2=-3 in 6
    replace y1=0 in 6
    replace y2=y[51] in 6

    replace x1=3 in 7
    replace x2=3 in 7
    replace y1=0 in 7
    replace y2=y[351] in 7

    replace x1=-4 in 8
    replace x2=4 in 8
    replace y1=0 in 8
    replace y2=0 in 8

    segments x1 y1 x2 y2

    gph text 10000 16000 0 0 34.13%
    gph text 10000 19000 0 0 34.13%

    gph text 18000 13000 0 0 13.59%
    gph text 18000 22500 0 0 13.59%

    gph text 19000 10000 0 0 2.15%
    gph text 19000 25500 0 0 2.15%
    gph close

    restore

end