*! version 1.0.0  14may1995
program define ttoz
        version 4.0

        preserve                   /*  Save all the current stata stuff */
        clear                      /*  Clear everything so no conflicts */

        global npts = 201
        global df=2

        quietly {
                set obs $npts
                gen x= .
                gen y = .}

        global D_sm1 "Xmin"
        global HJN_V1=-3.
        wdctl static D_sm1   5 5 25 10 
        wdctl edit   HJN_V1 35 5 20 10 

        global D_sm2 "Xmax"
        global HJN_V2=3.
        wdctl static D_sm2   5 20 25 10 
        wdctl edit   HJN_V2 35 20 20 10 

        global D_sm3 "df max"
        global HJN_V3=20
        wdctl static D_sm3   5 35 25 10 
        wdctl edit   HJN_V3 35 35 20 10 

        global D_sm4 "df"
        wdctl static D_sm4   5 95 30 12
        wdctl static df     35 95 30 12

        wdctl button "Run"       5 50 30 12 D_b1
        wdctl button "Close"     5 65 30 12 D_b2
        wdctl button "Help"      5 80 30 12 D_b3

        global D_b1 "ttozdr"
        global D_b2 "exit 1234"
        global D_b3 "whelp ttoz"

        cap noi wdlg "t -> Z" $D_dlgx $D_dlgy 70 120

        restore

end

program define ttozdr
    version 4.0

/* Get lower and upper x values and make sure they're legal */

    scalar x1 = $HJN_V1      
    scalar x2 = $HJN_V2

    local dfmax=$HJN_V3

    if x1>=x2 {              
        sstopbox stop "lower limit must be less than upper limit"
        exit}

    if `dfmax'<2 | `dfmax'>100 {
        sstopbox stop "dfmax must be between 2 and 100"
        exit}

    gph open
    gph pen 1

/* Get Z curve and plot it with graphics off to get scaling information */

    replace x = x1 + ((_n-1)/($npts-1))*(x2-x1)
    replace y = exp(-(x^2)/2)/sqrt(2*_pi)
    summarize y
    local ymax=_result(6)
    pdf_t x y 2
    summarize y
    local ymax1=_result(6)
    local ymax=max(`ymax',`ymax1')
    pdf_t x y 20
    summarize y
    local ymax1=_result(6)
    local ymax=max(`ymax',_result(6))
    local xmin=x1
    local xmax=x2


*    set graphics off
*    graph y x, c(l) s(i)  xlabel ylabel l1(" ") l2(" ") b1(" ") b2(" ")
*    set graphics on

*    local ymin = _result(1)
*    local ymax = _result(2)        
*    local xmin = _result(3)
*    local xmax = _result(4)

/* Now plot it for real */

    replace y = exp(-(x^2)/2)/sqrt(2*_pi)
    graph y x, c(l) s(i)  xlabel ylabel xscale(`xmin',`xmax') /*
         */ yscale(0,`ymax') l1(" ") l2(" ") b1(" ") b2(" ") pen(3)

/* Now plot t with 2 degrees of freedom so we can erase it at start of loop */

    global df=2
    pdf_t x y $df

    graph y x, c(l) s(i)  xlabel ylabel xscale(`xmin',`xmax') /*
          */ yscale(0,`ymax') l1(" ") l2(" ") b1(" ") b2(" ") pen(1)

/* Now do while loop over df */

    while $df <= `dfmax' {


/* Erase previous t pdf */

        graph y x, c(l) s(i)  xlabel ylabel xscale(`xmin',`xmax') /*
             */ yscale(0,`ymax') l1(" ") l2(" ") b1(" ") b2(" ") pen(0)

/* Get new t pdf and draw it */

        pdf_t x y $df

        graph y x, c(l) s(i)  xlabel ylabel xscale(`xmin',`xmax') /*
           */ yscale(0,`ymax') l1(" ") l2(" ") b1(" ") b2(" ") pen(1)

        wdupdate
        global df=$df+1
        

    }

    global df=`dfmax'

    gph text 1000 16000 0 0 t_`dfmax' and Z curves
    gph close

end