| Expensive loops... can they be avoided? [message #58910] |
Tue, 26 February 2008 01:41 |
Rainer
Messages: 5
Registered: November 2007
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Junior Member |
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Hi!
I need to render 2D slices cut from 3D spherical grid data. So far, I
am using a brute force method which, using two FOR loops, is
unfortunately rather slow (although working just fine). The problem
and my approach boil down to this:
-- A[i,j] is the input array, with r[i] and chi[j] being curvilinear
coordinates (not necessarily uniformly spaced)
-- B[k,l] is the output array with x[l] and y[l] being uniformly
spaced Cartesian coordinates (to be plotted with TVSCALE)
for k=0,nx-1 do begin
for l=0,ny-1 do begin
curr = sqrt(x[k]^2+y[l]^2)
curchi = atan(x[k],y[l])
if "curchi or curr are out of bounds" then begin
B[k,l] = environment_value
continue
endif
foo = min( r - curr ,nearestr,/absolute)
foo = min( chi - curchi ,nearestchi,/absolute)
B[k,l] = A[nearestr,nearestchi]
endfor
endfor
The calculation of "curr" and "curchi" can easily be done outside the
loops of course. But what can I do with the rest?
Thanks,
Rainer
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