*! version 1.1              08 September 1992 (STB-10: sg15)
program define spline
    version 3.0
         local i=`1'
         mac shift
        mac def _varlist "req ex min(1) max(1)"
        local if "opt"
        local in "opt"
        parse "`*'"
         if `i' <3 | `i' >7 {
              di in red "you must specify between 3 and 7 knots"
              di in gre "see help spline"
              error 198
         }
qui count `if' `in'
if _result(1)>99 {
    if `i'==3 {
         qui centile `1' `if' `in', centile(5 50 95)
         local knota=$S_7
         local knotb=$S_8
         local knotc=$S_9
         gen byte cut1=`1'>`knota'
         gen byte cut2=`1'>`knotb'
         gen byte cut3=`1'>`knotc'
#del ;
         gen double knot1=(((`1'-`knota')^3)*cut1)-
         ((((`1'-`knotb')^3)*cut2*(`knotc'-`knota'))/(`knotc'-`knotb'))+
         ((((`1'-`knotc')^3)*cut3*(`knotb'-`knota'))/(`knotc'-`knotb')) ;
#del cr
         drop cut1 cut2 cut3
    }
    else if `i'==4 {
         qui centile `1' `if' `in', centile(5 35 65 95)
         local knota=$S_7
         local knotb=$S_8
         local knotc=$S_9
         local knotd=$S_10
         gen byte cut1=`1'>`knota'
         gen byte cut2=`1'>`knotb'
         gen byte cut3=`1'>`knotc'
         gen byte cut4=`1'>`knotd'
#del ;
         gen double knot1=(((`1'-`knota')^3)*cut1)-
         ((((`1'-`knotb')^3)*cut2*(`knotc'-`knota'))/(`knotc'-`knotb'))+
         ((((`1'-`knotc')^3)*cut3*(`knotb'-`knota'))/(`knotc'-`knotb')) ;
         gen double knot2=(((`1'-`knotb')^3)*cut2)-
         ((((`1'-`knotc')^3)*cut3*(`knotd'-`knotb'))/(`knotd'-`knotc'))+
         ((((`1'-`knotd')^3)*cut4*(`knotc'-`knotb'))/(`knotd'-`knotc')) ;
#del cr
         drop cut1 cut2 cut3 cut4
    }
    else if `i'==5 {
         qui centile `1' `if' `in', centile(5 27.5 50 72.5 95)
         local knota=$S_7
         local knotb=$S_8
         local knotc=$S_9
         local knotd=$S_10
         local knote=$S_11
         gen byte cut1=`1'>`knota'
         gen byte cut2=`1'>`knotb'
         gen byte cut3=`1'>`knotc'
         gen byte cut4=`1'>`knotd'
         gen byte cut5=`1'>`knote'
#del ;
         gen double knot1=(((`1'-`knota')^3)*cut1)-
         ((((`1'-`knotb')^3)*cut2*(`knotc'-`knota'))/(`knotc'-`knotb'))+
         ((((`1'-`knotc')^3)*cut3*(`knotb'-`knota'))/(`knotc'-`knotb')) ;
         gen double knot2=(((`1'-`knotb')^3)*cut2)-
         ((((`1'-`knotc')^3)*cut3*(`knotd'-`knotb'))/(`knotd'-`knotc'))+
         ((((`1'-`knotd')^3)*cut4*(`knotc'-`knotb'))/(`knotd'-`knotc')) ;
         gen double knot3=(((`1'-`knotc')^3)*cut3)-
         ((((`1'-`knotd')^3)*cut4*(`knote'-`knotc'))/(`knote'-`knotd'))+
         ((((`1'-`knote')^3)*cut5*(`knotd'-`knotc'))/(`knote'-`knotd')) ;
#del cr
         drop cut1 cut2 cut3 cut4 cut5
    }
    else if `i'==6 {
         qui centile `1' `if' `in', centile(5 23 41 59 77 95)
         local knota=$S_7
         local knotb=$S_8
         local knotc=$S_9
         local knotd=$S_10
         local knote=$S_11
         local knotf=$S_12
         gen byte cut1=`1'>`knota'
         gen byte cut2=`1'>`knotb'
         gen byte cut3=`1'>`knotc'
         gen byte cut4=`1'>`knotd'
         gen byte cut5=`1'>`knote'
         gen byte cut6=`1'>`knotf'
#del ;
         gen double knot1=(((`1'-`knota')^3)*cut1)-
         ((((`1'-`knotb')^3)*cut2*(`knotc'-`knota'))/(`knotc'-`knotb'))+
         ((((`1'-`knotc')^3)*cut3*(`knotb'-`knota'))/(`knotc'-`knotb')) ;
         gen double knot2=(((`1'-`knotb')^3)*cut2)-
         ((((`1'-`knotc')^3)*cut3*(`knotd'-`knotb'))/(`knotd'-`knotc'))+
         ((((`1'-`knotd')^3)*cut4*(`knotc'-`knotb'))/(`knotd'-`knotc')) ;
         gen double knot3=(((`1'-`knotc')^3)*cut3)-
         ((((`1'-`knotd')^3)*cut4*(`knote'-`knotc'))/(`knote'-`knotd'))+
         ((((`1'-`knote')^3)*cut5*(`knotd'-`knotc'))/(`knote'-`knotd')) ;
         gen double knot4=(((`1'-`knotd')^3)*cut4)-
         ((((`1'-`knote')^3)*cut5*(`knotf'-`knotd'))/(`knotf'-`knote'))+
         ((((`1'-`knotf')^3)*cut6*(`knote'-`knotd'))/(`knotf'-`knote')) ;
#del cr
         drop cut1 cut2 cut3 cut4 cut5 cut6
    }
    else if `i'==7 {
         qui centile `1' `if' `in', centile(2.5 18.33 34.17 50 65.83 81.67 97.5)
         local knota=$S_7
         local knotb=$S_8
         local knotc=$S_9
         local knotd=$S_10
         local knote=$S_11
         local knotf=$S_12
         local knotg=$S_13
         gen byte cut1=`1'>`knota'
         gen byte cut2=`1'>`knotb'
         gen byte cut3=`1'>`knotc'
         gen byte cut4=`1'>`knotd'
         gen byte cut5=`1'>`knote'
         gen byte cut6=`1'>`knotf'
         gen byte cut7=`1'>`knotg'
#del ;
         gen double knot1=(((`1'-`knota')^3)*cut1)-
         ((((`1'-`knotb')^3)*cut2*(`knotc'-`knota'))/(`knotc'-`knotb'))+
         ((((`1'-`knotc')^3)*cut3*(`knotb'-`knota'))/(`knotc'-`knotb')) ;
         gen double knot2=(((`1'-`knotb')^3)*cut2)-
         ((((`1'-`knotc')^3)*cut3*(`knotd'-`knotb'))/(`knotd'-`knotc'))+
         ((((`1'-`knotd')^3)*cut4*(`knotc'-`knotb'))/(`knotd'-`knotc')) ;
         gen double knot3=(((`1'-`knotc')^3)*cut3)-
         ((((`1'-`knotd')^3)*cut4*(`knote'-`knotc'))/(`knote'-`knotd'))+
         ((((`1'-`knote')^3)*cut5*(`knotd'-`knotc'))/(`knote'-`knotd')) ;
         gen double knot4=(((`1'-`knotd')^3)*cut4)-
         ((((`1'-`knote')^3)*cut5*(`knotf'-`knotd'))/(`knotf'-`knote'))+
         ((((`1'-`knotf')^3)*cut6*(`knote'-`knotd'))/(`knotf'-`knote')) ;
         gen double knot5=(((`1'-`knote')^3)*cut5)-
         ((((`1'-`knotf')^3)*cut6*(`knotg'-`knote'))/(`knotg'-`knotf'))+
         ((((`1'-`knotg')^3)*cut7*(`knotf'-`knote'))/(`knotg'-`knotf')) ;
#del cr
         drop cut1 cut2 cut3 cut4 cut5 cut6 cut7
    }
}
else {
    if `i'==3 {
         qui centile `1' `if' `in', centile(50)
         if "`if'"!="" | "`in'"!="" { qui keep `if' `in' }
         sort `1'
         local knota=`1'[5]
         local knotb=$S_7
         local knotc=`1'[_N-5]
         gen byte cut1=`1'>`knota'
         gen byte cut2=`1'>`knotb'
         gen byte cut3=`1'>`knotc'
#del ;
         gen double knot1=(((`1'-`knota')^3)*cut1)-
         ((((`1'-`knotb')^3)*cut2*(`knotc'-`knota'))/(`knotc'-`knotb'))+
         ((((`1'-`knotc')^3)*cut3*(`knotb'-`knota'))/(`knotc'-`knotb')) ;
#del cr
         drop cut1 cut2 cut3
    }
    else if `i'==4 {
         qui centile `1' `if' `in', centile(35 65)
         if "`if'"!="" | "`in'"!="" { qui keep `if' `in' }
         sort `1'
         local knota=`1'[5]
         local knotb=$S_7
         local knotc=$S_8
         local knotd=`1'[_N-5]
         gen byte cut1=`1'>`knota'
         gen byte cut2=`1'>`knotb'
         gen byte cut3=`1'>`knotc'
         gen byte cut4=`1'>`knotd'
#del ;
         gen double knot1=(((`1'-`knota')^3)*cut1)-
         ((((`1'-`knotb')^3)*cut2*(`knotc'-`knota'))/(`knotc'-`knotb'))+
         ((((`1'-`knotc')^3)*cut3*(`knotb'-`knota'))/(`knotc'-`knotb')) ;
         gen double knot2=(((`1'-`knotb')^3)*cut2)-
         ((((`1'-`knotc')^3)*cut3*(`knotd'-`knotb'))/(`knotd'-`knotc'))+
         ((((`1'-`knotd')^3)*cut4*(`knotc'-`knotb'))/(`knotd'-`knotc')) ;
#del cr
         drop cut1 cut2 cut3 cut4
    }
    else if `i'==5 {
         qui centile `1' `if' `in', centile(27.5 50 72.5)
         if "`if'"!="" | "`in'"!="" { qui keep `if' `in' }
         sort `1'
         local knota=`1'[5]
         local knotb=$S_7
         local knotc=$S_8
         local knotd=$S_9
         local knote=`1'[_N-5]
         gen byte cut1=`1'>`knota'
         gen byte cut2=`1'>`knotb'
         gen byte cut3=`1'>`knotc'
         gen byte cut4=`1'>`knotd'
         gen byte cut5=`1'>`knote'
#del ;
         gen double knot1=(((`1'-`knota')^3)*cut1)-
         ((((`1'-`knotb')^3)*cut2*(`knotc'-`knota'))/(`knotc'-`knotb'))+
         ((((`1'-`knotc')^3)*cut3*(`knotb'-`knota'))/(`knotc'-`knotb')) ;
         gen double knot2=(((`1'-`knotb')^3)*cut2)-
         ((((`1'-`knotc')^3)*cut3*(`knotd'-`knotb'))/(`knotd'-`knotc'))+
         ((((`1'-`knotd')^3)*cut4*(`knotc'-`knotb'))/(`knotd'-`knotc')) ;
         gen double knot3=(((`1'-`knotc')^3)*cut3)-
         ((((`1'-`knotd')^3)*cut4*(`knote'-`knotc'))/(`knote'-`knotd'))+
         ((((`1'-`knote')^3)*cut5*(`knotd'-`knotc'))/(`knote'-`knotd')) ;
#del cr
         drop cut1 cut2 cut3 cut4 cut5
    }
    else if `i'==6 {
         qui centile `1' `if' `in', centile(23 41 59 77)
         if "`if'"!="" | "`in'"!="" { qui keep `if' `in' }
         sort `1'
         local knota=`1'[5]
         local knotb=$S_7
         local knotc=$S_8
         local knotd=$S_9
         local knote=$S_10
         local knotf=`1'[_N-5]
         gen byte cut1=`1'>`knota'
         gen byte cut2=`1'>`knotb'
         gen byte cut3=`1'>`knotc'
         gen byte cut4=`1'>`knotd'
         gen byte cut5=`1'>`knote'
         gen byte cut6=`1'>`knotf'
#del ;
         gen double knot1=(((`1'-`knota')^3)*cut1)-
         ((((`1'-`knotb')^3)*cut2*(`knotc'-`knota'))/(`knotc'-`knotb'))+
         ((((`1'-`knotc')^3)*cut3*(`knotb'-`knota'))/(`knotc'-`knotb')) ;
         gen double knot2=(((`1'-`knotb')^3)*cut2)-
         ((((`1'-`knotc')^3)*cut3*(`knotd'-`knotb'))/(`knotd'-`knotc'))+
         ((((`1'-`knotd')^3)*cut4*(`knotc'-`knotb'))/(`knotd'-`knotc')) ;
         gen double knot3=(((`1'-`knotc')^3)*cut3)-
         ((((`1'-`knotd')^3)*cut4*(`knote'-`knotc'))/(`knote'-`knotd'))+
         ((((`1'-`knote')^3)*cut5*(`knotd'-`knotc'))/(`knote'-`knotd')) ;
         gen double knot4=(((`1'-`knotd')^3)*cut4)-
         ((((`1'-`knote')^3)*cut5*(`knotf'-`knotd'))/(`knotf'-`knote'))+
         ((((`1'-`knotf')^3)*cut6*(`knote'-`knotd'))/(`knotf'-`knote')) ;
#del cr
         drop cut1 cut2 cut3 cut4 cut5 cut6
    }
    else if `i'==7 {
         qui centile `1' `if' `in', centile(18.33 34.17 50 65.83 81.67)
         if "`if'"!="" | "`in'"!="" { qui keep `if' `in' }
         sort `1'
         local knota=`1'[5]
         local knotb=$S_7
         local knotc=$S_8
         local knotd=$S_9
         local knote=$S_10
         local knotf=$S_11
         local knotg=`1'[_N-5]
         gen byte cut1=`1'>`knota'
         gen byte cut2=`1'>`knotb'
         gen byte cut3=`1'>`knotc'
         gen byte cut4=`1'>`knotd'
         gen byte cut5=`1'>`knote'
         gen byte cut6=`1'>`knotf'
         gen byte cut7=`1'>`knotg'
#del ;
         gen double knot1=(((`1'-`knota')^3)*cut1)-
         ((((`1'-`knotb')^3)*cut2*(`knotc'-`knota'))/(`knotc'-`knotb'))+
         ((((`1'-`knotc')^3)*cut3*(`knotb'-`knota'))/(`knotc'-`knotb')) ;
         gen double knot2=(((`1'-`knotb')^3)*cut2)-
         ((((`1'-`knotc')^3)*cut3*(`knotd'-`knotb'))/(`knotd'-`knotc'))+
         ((((`1'-`knotd')^3)*cut4*(`knotc'-`knotb'))/(`knotd'-`knotc')) ;
         gen double knot3=(((`1'-`knotc')^3)*cut3)-
         ((((`1'-`knotd')^3)*cut4*(`knote'-`knotc'))/(`knote'-`knotd'))+
         ((((`1'-`knote')^3)*cut5*(`knotd'-`knotc'))/(`knote'-`knotd')) ;
         gen double knot4=(((`1'-`knotd')^3)*cut4)-
         ((((`1'-`knote')^3)*cut5*(`knotf'-`knotd'))/(`knotf'-`knote'))+
         ((((`1'-`knotf')^3)*cut6*(`knote'-`knotd'))/(`knotf'-`knote')) ;
         gen double knot5=(((`1'-`knote')^3)*cut5)-
         ((((`1'-`knotf')^3)*cut6*(`knotg'-`knote'))/(`knotg'-`knotf'))+
         ((((`1'-`knotg')^3)*cut7*(`knotf'-`knote'))/(`knotg'-`knotf')) ;
#del cr
         drop cut1 cut2 cut3 cut4 cut5 cut6 cut7
    }
}
    noi di ""
    noi di "for test of functional form use testparm `1' kn*"
    noi di "for possible help in transforming, obtain the predicted values,"
    noi di "using fpredict, and then gr pred.val by `1'"
end