Re: Fast matrix filling in IDL

[Phillip & Suzanne David <pdavid(at)earthling.net>]

David Fanning wrote:
> 
> Stein Vidar Hagfors Haugan (steinhh@ulrik.uio.no) writes:
> >
> > A slight modification of David's program, and adding
> > my favourite speedup method:
> >
> >   time = systime(1)
> >   array = rebin(reform(v,m,1,/overwrite),m,n,/sample)
> >   print, 'Time for Rebin Operations: ', systime(1) - time
> >
> > On { alpha OSF unix 5.2 Oct 30 1998}, this gives:
> >
> > Time for Loop:                   0.27343702
> > Time for Matrix Operations:      0.093750000
> > Time for Rebin Operations:       0.067382932
> >
> > Note that the relative speeds can vary quite a lot on
> > different architectures.
> 
> I guess. Here is what I get with Stein Vidar's modifications
> on my Windows NT machine:
> 
>    IDL> Print, !Version
>    { x86 Win32 Windows 5.2 Oct 30 1998}
>    IDL> test
>    Time for Loop:       0.10000002
>    Time for Matrix Operations:      0.019999981
>    Time for Rebin Operations:      0.039999962
> 
> The Rebin operations are twice as slow as the matric operations.
> Hummm. Why!?


Here's another result from IDL 5.0.2 on the Mac:
Time for Loop:       0.30000007
Time for Matrix Operations:       0.13333333
Time for Rebin Operations:       0.50000000

Phillip