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*Subject*: Re: Zero... THANKS Pavel and J.D.*From*: Frank Morgan <frank.morgan(at)jhuapl.edu>*Date*: Thu, 01 Jul 1999 12:19:37 -0700*Newsgroups*: comp.lang.idl-pvwave*Organization*: Johns Hopkins University Applied Physics Lab, Laurel, MD, USA*References*: <37780A83.3310ECE@jhuapl.edu>*Xref*: news.doit.wisc.edu comp.lang.idl-pvwave:15505

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

**References**:**Zero vector detection in IDL***From:*Frank Morgan

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