*! version 3.0.0  10/22/93                      STB-24: snp7.1
program define spbase
if "`*'"=="" {
    di in bl "-> spline xvar [if] [in] [, [gen(basis_name)]"
    di in bl _skip(10) "[Nknots(#)] [Knots(#...#)]]"
                exit 198
}
        version 3.0
        local varlist "req ex min(1) max(1)"
        local if "opt"
        local in "opt"
        local options "GEN(string) Nknots(int 0) Knots(string) "
        parse "`*'"
        if "`gen'"=="" {
                di in red "Must specify name for basis"
		exit 198
	}
        parse "`varlist'", parse(" ")
        tempvar  X 
        quietly {
                gen `X'=`1' `if' `in'
                count if `X'<.
                local cnt = _result(1)
                if `cnt'<3 { noisily error 2001 }
                local x "`1'"
                _crcslbl `X' `1'
                sort `X'
                local kN = `X'[`cnt']
		local k0=`X'[1]
* GENERATE INTERIOR KNOTS  
                if "`knots'"=="" {
                        local nk = `nknots'
                        if `nk' == 0 {
                                local nk = int((`cnt')^.25)
                        }
                        local j = `nk' 
                        while `j' > 0 {
                                local k`j'=`X'[int((`j'*`cnt'/(`nk'+1))+.5)]
                                local j = `j' -1
                        }
                }
                else {
                        parse "`knots'", parse(" ,")
                        local nk = 0
                        while "`1'"!="" {
			   if "`1'"!=","{
			    	if `1'<`k0' | `1'>`kN' {
					noisily di "knot at `1' ignored"}
			    	else {
                                	local nk = `nk' + 1
					local k`nk' = `1' 
			    	}
			   }
                           macro shift
                        }
                }
* CREATE REGRESSION VARIABLES
                local j = 1
		local gen1 "`x'" 
                while `j' <= `nk' {
		   confirm new var `gen'`j'
        	   #delimit ;
                   gen `gen'`j'= -((`kN'-`k`j'')/(`kN'-`k0'))*(`X'-`k0')^3 ;
/* old    replace `gen'`j'=`gen'`j'+(`X'-`k`j'')^3 if `X'>`k`j'' ; */
                   replace `gen'`j'=`gen'`j'+(`X'-`k`j'')^3 if `X'>`k`j'' & `k`j'' > `k0' ;
                   replace `gen'`j'=(`kN'-`k`j'')*(`k`j''-`k0')
				*(`kN'+`k`j''+`k0'-3*`X')	if `X'>`kN' ;
        	   #delimit cr
		   lab var `gen'`j' "(`x'-k`j') cubed"
	           local gen1 "`gen1' `gen'`j'"
                   local j = `j' +1
                }
		mac def `gen' "`gen1'"
	}
end