st: Why `sums'[_N] in stata module kernreg1

[Yibing Wang <wang_yibing@yahoo.com>]

Dear Statalisters,

I tried to use the Stata module kernreg1 
(KERNREG1: Stata module to compute kernel regression
(Nadaraya-Watson estimator)
http://ideas.repec.org/s/boc/bocode1.html)

program define kernreg1
  version 3.1

...
...

while `count'<=`np' {
    replace `xo'=`gridp'[`count']
    replace `z'=(`xo'-`xvar')/`h'
    if `kc'==1 {
        replace `kz'=0.5 if abs(`z')<=1 & `use'
    }
    else if `kc'==2 {
        replace `kz'=(1-abs(`z')) if abs(`z')<=1 &
`use'
    }
    ...
    ... 
    
    replace `sums'= sum(`kz')
    replace `sums2'= sum(`kzy')
    replace `fh'=(1/(`nuobs'*`h'))*`sums'[_N] if
_n==`count'
    replace `rh'=(1/(`nuobs'*`h'))*`sums2'[_N] if
_n==`count'
    replace `kz'=0
    replace `kzy'=0
    replace `count'=`count'+1
  }

  if `rh'==0 {
          replace `mh'=0
  }
  else {
          replace `mh'=`rh'/`fh'
  }


My question is why `sums'[_N] is used instead of
`sums' as we are trying to calculate fh from 1 to _N ?

I have been trying to figure it out without success,
can anybody give me some advice?

Any suggestion is highly appreciated,

Thanks,

Yibing

University of Calgary


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