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Re: fast search [message #50778]

Wed, 18 October 2006 08:25

greg michael
Messages: 163
Registered: January 2006

Senior Member

All but one indestructible loop removed. Wish I had a use for this
program now... hope it's useful to you, Marie!

pro splitsearch3,p,dist
;recursively splits the search volume into n_split^3 subvolumes. When
;there are fewer than 'threshold' points
;in a subvolume, checks for matches the brute force way - every point
;against every other.

n_split=4 ;1-D cutting factor (for 3, cube is cut into 3x3x3=27
subvolumes)
threshold=75 ;no. of points to start pairwise comparison
n=n_elements(p)

if n gt threshold then begin
mxx=max(p.x,min=mnx)
mxy=max(p.y,min=mny)
mxz=max(p.z,min=mnz)
bx=fix((p.x-mnx)/(mxx-mnx)*n_split)<(n_split-1) ;< to ensure max
element not in new bin
by=fix((p.y-mny)/(mxy-mny)*n_split)<(n_split-1)
bz=fix((p.z-mnz)/(mxz-mnz)*n_split)<(n_split-1)
b=bx+by*n_split+bz*n_split^2
h=histogram(b,min=0,reverse_indices=ri)

for i=0,n_elements(h)-1 do begin
if ri[i] ne ri[i+1] then begin
q=[ri[ri[i]:ri[i+1]-1]]
if n_elements(q) ge 2 then splitsearch3,p[q],dist ;splitsearch
again, if enough to compare
endif
endfor

endif else begin
q1=rebin(indgen(n),n,n) ;set up indices for pairwise matching
q2=transpose(q1)
d=sqrt((p[q1].x-p[q2].x)^2+(p[q1].y-p[q2].y)^2+(p[q1].z-p[q2 ].z)^2)
;calculate pair distances
i=where((d le dist) and (q1 gt q2)) ;select close neigbours (q1>q2 to
avoid reverse pairs)
if i[0] ne -1 then print,p[q1[i]],p[q2[i]] ;print the neighbours, if
found
endelse
end

IDL> p=ss_makegalaxies(5e6)
IDL> splitsearch3,p,.02
{ 915.876 843.515 319.991}{ 915.861 843.528
319.994}

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[Message index]

		Re: fast search By: greg michael on Wed, 18 October 2006 08:25
		Re: fast search By: greg michael on Tue, 17 October 2006 11:25
		Re: fast search By: greg michael on Tue, 17 October 2006 10:17
		Re: fast search By: greg michael on Tue, 17 October 2006 07:15
		Re: fast search By: Paolo Grigis on Tue, 17 October 2006 05:53
		Re: fast search By: m.goullant@gmail.com on Thu, 19 October 2006 04:01
		Re: fast search By: m.goullant@gmail.com on Thu, 19 October 2006 03:46

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