| Re: Improving a piece of code with arrays and for-loops [message #52461 is a reply to message #52460] |
Thu, 08 February 2007 09:53   |
Vince Hradil
Messages: 574
Registered: December 1999
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Senior Member |
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On Feb 8, 7:23 am, "Halfdan" <halfd...@gmail.com> wrote:
> Hello
>
> I have been looking at my same piece of IDL-code for quite a while now
> and I have yet not found any good method to improve it. I want to
> improve the speed and rid the code of the nested for-loops. Maybe
> there is someone here who has good ideas and is willing to point me in
> the right direction?
>
> The problematic code is below. It is a part of a method to estimate
> wind gusts in output from an atmospheric model. The i and j
> dimensions are the x- and y-locations of the model-points in the
> horizontal and s are the model level heights in the vertical (starting
> from the model top and growing towards the surface).
>
> The code works in the vertical, starting from the surface (largest
> value of s) and works upwards (towards smaller s) to where the value
> of the variable tke is less than tkelvl or tke_diff is less than a
> very small number. The code has to do the following three things:
>
> 1. Choose the greatest value of wsp (windspeed) where the value of
> int_diff exceeds 0.
> 2. Choose the greatest value of wsp where the value of int_diffver
> exceeds 0.
> 3. Choose the greatest value of wsp.
>
> This has to be repeated for every grid-point in the horizontal (I have
> to assume that I have very little a priori knowledge of the behaviour
> of any of my variables at any gridpoint and model height).
>
> Any ideas on improving this?
>
> Thanks in advance,
> Halfdan
>
> ps. The problematic code:
>
> for i=1,ni-2 do begin
> for j=1, nj-2 do begin
> s = ns-1
> REPEAT BEGIN
> if int_diff(i,j,s) GE 0. AND wsp(i,j,s) GT fgtmp(i,j,
> 0) then $
> fgtmp(i,j,0) = wsp(i,j,s)
> if wsp(i,j,s) GT fgtmp(i,j,1) then $
> fgtmp(i,j,1) = wsp(i,j,s)
> if int_diffver(i,j,s) GE 0. AND wsp(i,j,s) GT
> fgtmp(i,j,2) then $
> fgtmp(i,j,2) = wsp(i,j,s)
> s=s-1
> ENDREP UNTIL tke(i,j,s) LT tkelvl(i,j) OR
> tke_diff(i,j,s) LT eps
> endfor
> endfor
First thing that comes to mind is the invert the loop order. Granted
I've spent about 30 s looking at this, though.
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