| Re: Zero... THANKS Pavel and J.D. [message #16156] |
Fri, 02 July 1999 00:00 |
R.Bauer
Messages: 1424
Registered: November 1998
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Senior Member |
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Frank Morgan wrote:
> Pavel and J.D.,
>
> Thanks to both of you for some useful information.
>
> Pavel mentioned the 0-at-the-end problem with the loop approach. After some
> analysis of my problem (a directed graph search), I've discovered that most
> of the vectors I search will contain a non-zero within the first 10% or so
> of the length. I would have thought then that the loop would be faster
> than 'where' but J.D.'s timing results prove me wrong - looks like even with
> loop halt at 10% (where his test halted at 50%), the timing would be 0.99/5
> = 0.2, still twice the time of 'where' searching the whole vector - boy, IDL
> loops really are bad!
>
> For now I'm settling on 'where' - it's just fast enough for the biggest
> graphs I'm searching so far. J.D.'s timing for external code indicates that
> with 10% lengths typical, I might get 10X speedup over 'where' but for now
> the DLL compilation isn't worth it. But it gives me an out if I need to
> search bigger graphs.
>
> Incedentally, I'd never realized you can say (where())[0] to get that first
> element - that's a handy statement.
It is always better to use the count value.
where(a eq 0 ,count)
if count gt 0 then ...
R.Bauer
>
>
> Thaks,
> Frank
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| Re: Zero... THANKS Pavel and J.D. [message #16168 is a reply to message #16156] |
Thu, 01 July 1999 00:00  |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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Frank Morgan (frank.morgan@jhuapl.edu) writes:
> Incedentally, I'd never realized you can say (where())[0] to get that first
> element - that's a handy statement.
Handy, but really, really dangerous. I wouldn't use it in
code, personally, unless I had bomb-proof error handling
in place. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
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| Re: Zero... THANKS Pavel and J.D. [message #16172 is a reply to message #16168] |
Thu, 01 July 1999 00:00 |
Frank Morgan
Messages: 3
Registered: June 1999
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Junior Member |
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Pavel and J.D.,
Thanks to both of you for some useful information.
Pavel mentioned the 0-at-the-end problem with the loop approach. After some
analysis of my problem (a directed graph search), I've discovered that most
of the vectors I search will contain a non-zero within the first 10% or so
of the length. I would have thought then that the loop would be faster
than 'where' but J.D.'s timing results prove me wrong - looks like even with
loop halt at 10% (where his test halted at 50%), the timing would be 0.99/5
= 0.2, still twice the time of 'where' searching the whole vector - boy, IDL
loops really are bad!
For now I'm settling on 'where' - it's just fast enough for the biggest
graphs I'm searching so far. J.D.'s timing for external code indicates that
with 10% lengths typical, I might get 10X speedup over 'where' but for now
the DLL compilation isn't worth it. But it gives me an out if I need to
search bigger graphs.
Incedentally, I'd never realized you can say (where())[0] to get that first
element - that's a handy statement.
Thaks,
Frank
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