Re: speed up maxind loop?

Hello,

This is an instance where I would likely recommend using
a shared object code [fortran or C].

D
On 12/18/2010 01:54 AM, Seifert Axel wrote:
>
> Will,
>
> Thanks for your comment. But before writing my own dim_maxind_n I
> thought I could ask whether somebody else already stumbled across this
> issue. Measuring layer thicknesses seems not such an uncommon problem.
>
> The reversal of the coordinate in minind(cwc(kwmax(j,i):0,j,i) is not a
> typo, because minind returns the index of the FIRST occurrence of a
> minimum value, i.e.
>
> ncl 0> a = (/3,2,1,0,0,0/)
> ncl 1> print(minind(a(0:)))
> (0) 3
> ncl 2> print(minind(a(:0)))
> (0) 0
>
> Nevertheless, thanks for trying to help.
>
> I should have mentioned that I do mask the w array before the loop
>
> ; mask vertical velocity as conditional sampling of deep convection
> ; (1) w larger than 1 m/s
> ; (2) cloud water larger than 0.5 g/kg
> ; (3) CAPE larger than 10 J/kg
>
> w = mask(w,cwc.lt.0.5e-3.or.w.lt.1,False)
> w = mask(w,cape.lt.10,False)
>
> Maybe ind_resolve could be used to collapse the double-loop over the
> whole array into a single-loop over the relevant columns? Thats at least
> what I would try on a vector machine. Would this help to speed up ncl, too?
>
> Axel
>
>
>
>
> -----Ursprüngliche Nachricht-----
> Von: ncl-talk-bounces@ucar.edu im Auftrag von Hobbs, Will R (3244-CalTech)
> Gesendet: Fr 17.12.2010 19:36
> An: Axel Seifert; ncl-talk
> Betreff: Re: [ncl-talk] speed up maxind loop?
>
> Axel
>
> You have a couple of options; the first being to write your own
> dim_maxind_n function!
>
> The second would be to remove as many operations as possible from the
> loop; for example the statement ' zcdepth(j,i) = (/ zctop(j,i) -
> zcbase(j,i) /)' would be better after the loop has closed. There are a
> few places where you could do similar things (another example is
> subtracting 1e-6 from cwc before the loop starts; that's one operation
> as opposed to xdim*ydim operations).
>
> I also notice an error in one of your lines that might be really slowing
> you down:
>
> ktop(j,i) = kwmax(j,i) - minind(cwc(kwmax(j,i):0,j,i) - 1e-6)
>
> SHOULD read:
>
> ktop(j,i) = kwmax(j,i) - minind(cwc(0:kwmax(j,i),j,i) - 1e-6) ;order of
> the zero in indexing cwc has changed.
>
>
> I 'speculate' that because the indexing has been inverted, NCL might be
> doing an unnecessary reversal at every time step
>
>
> Will
>
>
>
> On 12/17/10 6:57 AM, "Axel Seifert" <Axel.Seifert@dwd.de> wrote:
>
>
>
> Hi NCL folks:
>
> I am using maxind and minind to measure cloud depth in CRM data. This
> works fine, but it is kind of slow. Unfortunately, maxind and minind do
> not support multidimensional arrays. There is no dim_maxind_n available,
> is there?
>
> This is the loop that I want to speed up (I have some TB of data to
> analyze):
>
> print(" calculate convective cloud depth (please be patient, this can be
> slow)")
> do i=0,xdim-1
> do j=0,ydim-1
>
> ; find maximum of vertical velocity in the updraft
> kwmax(j,i) = maxind(w(:,j,i))
>
> if (.not.ismissing(kwmax(j,i))) then
> ; find cloud top and cloud base starting from max updraft position
> ktop(j,i) = kwmax(j,i) - minind(cwc(kwmax(j,i):0,j,i) - 1e-6)
> kbase(j,i) = kwmax(j,i) + minind(cwc(kwmax(j,i):,j,i) - 1e-6)
>
> ; store geometric height of cloud base, top and depth
> zctop(j,i) = (/ z(ktop(j,i),j,i) /)
> zcbase(j,i) = (/ z(kbase(j,i),j,i) /)
> zcdepth(j,i) = (/ zctop(j,i) - zcbase(j,i) /)
> end if
>
> end do
> end do
>
> Cheers, Axel
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Received on Mon Dec 20 09:49:30 2010