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Re: st: looping with geodist


From   Austin Nichols <austinnichols@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: looping with geodist
Date   Fri, 7 May 2010 11:25:32 -0400

Frederick Guy <f.guy@bbk.ac.uk>  :
Except that r(min) should be r(sum), of course.

On Fri, May 7, 2010 at 11:23 AM, Austin Nichols <austinnichols@gmail.com> wrote:
> conserve memory.  Suppose you want the weighted sum of inverse
> distances (assuming none are zero); then you could just:
>
> use type_i, clear
> local Ni=_N
> merge using type_j
> g w=.
> qui forv i=1/`Ni' {
> g double L=(yj-yi[`i'])*_pi/180
> replace L=(yj-yi[`i']-360)*_pi/180 if L<. & L>_pi
> replace L=(yj-yi[`i']+360)*_pi/180 if L<-_pi
> local t1 acos(sin(xj*_pi/180)*sin(xi[`i']*_pi/180)
> g i=1/(`t1'+cos(xj*_pi/180)*cos(xi[`i']*_pi/180)*cos(L))*6367.44)
> su i, meanonly
> replace w=r(min) in `i'
> drop L i
> }
> la var w "Sum of Inverse (Approx) Distances"

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