program define _ksmwrk
version 2.1
/*
        Args: 1=Y, 2=X, 3=count, 4=bandwidth, 5=smoothed Y,
        6=0 (unwtd mean), 1(unwtd line), 2(wtd mean), 3(wtd line).
        NOTE: bandwidth is expressed as a fraction of the sample size,
        not a number of sample values.
*/
        capture drop _W
        capture drop %_5
        capture {
/*
        Using symmetric neighbourhoods.
        %_k is half-bandwidth. Initialise using points 1,...,k+1.
        Delta is distance between current Y and furthest neighbour in the
        interval. _W is tricube weight function within the interval.
*/
                gen _W = 1
                gen %_5 = .
                mac def _wtd = (%_6>1)
                mac def _mean = (%_6==0 | %_6==2)
                mac def _k = int((%_4*%_3-0.5)/2)
                mac def _i 0
                while %_i<%_3 {
                        mac def _i = %_i+1
                        mac def _x0 = %_2[%_i]
			mac def _imk = max(1, %_i-%_k)
			mac def _ipk = min(%_i+%_k, %_3)
                        if %_wtd {
				#delimit ; 
                                mac def _delta = 1.0001*
					max(%_2[%_ipk]-%_x0, %_x0-%_2[%_imk]);
                                replace _W = (1-(abs(%_2-%_x0)/%_delta)^3)^3 
					in %_imk/%_ipk ;
				#delimit cr
                        }
                        if %_mean {
                                sum %_1 =_W in %_imk/%_ipk
                                replace %_5 = _result(3) in %_i
                        }
                        else {
                                reg %_1 %_2 =_W in %_imk/%_ipk
                                replace %_5 = _b[_cons]+_b[%_2]*%_x0 in %_i
                        }
                }
        	drop _W
        	exit
        }
        exit _rc
end