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Re: Fast matrix filling in IDL
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