program define chisq
        version 4.0

        preserve
        clear

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

        global df=10

        wdctl button "Reset"   15  5 25 12 HJN_B0
        wdctl button "df +"   15 20 25 12 HJN_B1
        wdctl button "df -"   15 35 25 12 HJN_B2
        wdctl button "Help"    15 50 25 12 HJN_B5
        wdctl button "Close"   15 65 25 12 HJN_B6

        global D_sm1 "Inc"
        global dfinc=10
        wdctl static D_sm1  3 110 10 10 
        wdctl edit   dfinc 15 110 25 10         
        
        global D_sm2 "df:"
        wdctl static D_sm2    15 125 15 12
        wdctl static df      35 125 15 12



        global HJN_B0 "chisqdr 0"
        global HJN_B1 "chisqdr 1"
        global HJN_B2 "chisqdr -1"
        global HJN_B5 "whelp chisq"
        global HJN_B6 "exit 1234"

        gph open

        chisqdr 0

        noi wdlg "Chi-square Curves"  5 5 80 165

        gph close

        restore

end

program define chisqdr
        version 4.0

        local arg=`1'

        if `arg'!=0 {
            graph y x, xlab(0,25,50,75,100,125,150) ylab(0,.025,.050,.075,.100) xscale(0,150) yscale(0,.1) c(l) s(i) l1(" ") l2(" ") b1(" ") b2(" ") pen(3)}
                
        if `arg'==0 { 
                global df=10
                gph close 
                gph open}

        if `arg'==1 {
                global df = min(100,$df+$dfinc)}

        if `arg'==-1 {
                global df = max(10,$df-$dfinc)}

        local xmin=invnchi($df,0,.001)
        local xmax=min(invnchi($df,0,.999),150)
        replace x=`xmin'+(`xmax'-`xmin')*(_n-1)/(_N-1)
        pdf_chi2 x y $df

        graph y x, xlab(0,25,50,75,100,125,150) ylab(0,.025,.050,.075,.100) xscale(0,150) yscale(0,.1) c(l) s(i) l1(" ") l2(" ") b1(" ") b2(" ") pen(2)
        gphconv
        summarize y
        local yy=_result(6)+.001
        local xx=$df-1
        drtext `xx' `yy'  0 "$df"

        
end

exit