program define scatt2
    version 4.0        
        
    preserve
    clear

    global np=0
    quietly{
        set obs 600
        gen x=.
        gen y=.}

    global D_sm11 "   This lab lets you experiment with different values of n and rho. Every time you click on Run you get a new scatterplot. You can try out different values of rho and n and see what effect they have. Note that you can keep the graphics window in the front and still be able to change rho and n and click on Run."
    wdctl static D_sm11 5 5 270 40
    
    global D_sm12 "Things to Notice: 1) Positive (negative) values of rho mean the points fall close to a line having positive (negative) slope, 2) The closer rho is to +1 or -1, the closer the points are to the line. 3) For values of rho between about -.4 to +.4, the scatterplots look very similar unless n is quite large."
    wdctl static D_sm12 5 50 270 40



    global HJN_V1 = 100
    global HJN_1 "n"
    wdctl static HJN_1   5 92 10 8
    wdctl edit   HJN_V1  20 92 20 8

    global HJN_V2 = 0
    global HJN_2 "Rho"
    wdctl static HJN_2   50 92 20 8
    wdctl edit   HJN_V2  75 92 20 8
        
        wdctl button "Run"    125 90 25 12 HJN_B2
        wdctl button "Close"  155 90 25 12 HJN_B3
        wdctl button "Help"   185 90 25 12 HJN_B4

    global HJN_B2 "scatt2dr"
    global HJN_B4 "whelp scatt2"
    global HJN_B3 "exit 1234"

    gph open
    gph pen 1        

    scatt2dr
    global HJN_V2=.9
    scatt2dr    
    global HJN_V2=-.9
    scatt2dr    
    global HJN_V2=.99
    scatt2dr    
        
    noi wdlg "Scatterplots, II"  5 150 280 120

    gph close

    restore
end

program define scatt2dr
    version 4.0

    local n=$HJN_V1
    local rho=$HJN_V2

    if `n' < 2 | `n' > 600 {
        sstopbox stop "sample size must be between 2 and 600"
        exit}

    if `rho' <= -1 | `rho'  >= 1 {
        sstopbox stop "rho must be between -1 and 1"
        exit}

    global np=$np+1


*    gph text 500 5000 0 0 `n' `rho' $np

    local np1=$np
    if `np1'==5 {
        gph close
        gph open
        gph pen 1
        global np=1
        local np1=1}

*    gph text 2000 5000 0 0 `np1'

    local nx1=int((`np1'-1)/2)*15000
    local nx2=`nx1'+15000
    local ny1=mod(`np1'-1,2)*11000
    local ny2=`ny1'+11000
    local nx=int((`nx1'+`nx2')/2)
    local ny=`ny1'+500

*    gph text 3000 5000 0 0 `nx1' `nx1' `ny1' `ny2' `nx' `ny'

    replace x=.
    replace y=.

    replace x = invnorm(uniform()) in 1/`n'
    replace y = `rho'*x + sqrt(1.0-`rho'*`rho')*invnorm(uniform()) in 1/`n'

    graph y x, xlab(-3,0,3) ylab(-3,0,3) xscale(-3,3) s(o) /*
        */ yscale(-3,3) bbox(`ny1',`nx1',`ny2',`nx2',850,400,0)

    local mrho: display %4.2f `rho'
    gph text `ny' `nx' 0 0 rho = `mrho'

end
exit