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*Subject*: Re: IDL FFT vs C benchmark?*From*: "David McClain" <dmcclain(at)azstarnet.com>*Date*: Mon, 7 Feb 2000 00:42:03 -0700*Newsgroups*: comp.lang.idl-pvwave*Organization*: Posted via Supernews, http://www.supernews.com*References*: <87engh$t1a$1@houston.jhuapl.edu>*Xref*: news.doit.wisc.edu comp.lang.idl-pvwave:18296

Actually, the IDL routines are pretty slow by comparison... More than two years ago I investigated their performance compared to the Intel Math Kernel Library and found that unlike the expected 2N log2 N for an NxN square image 2-D FFT, the IDL routines scaled as (N log2 N)^2 which implies a tree search on every butterfly operation. This appaling behavior was pointed out the RSI and they furnished the header comments from a Fortran reference that they used for their implementation. It appears that they sacrificed speed for the sake of arbitrary dimension FFT's. The Intel routines are strictly power of 2 but so what. I would rather have an interpolated transform to a power of 2 in size at expected speeds than to sacrifice performance due to poor scaling of the original problem. We now use the Intel MKL routines wrapped in a multithreaded DLL to maximize parallel performance of FFT's. The speedup is remarkable indeed. On our old 4-processor Pentium Pro machine we reached speeds of 75 MButterflys/sec. Our newer multiprocessors exceed that by another factor of 2-5. By comparison, we never saw the RSI routines exceed 7-10 MButterflys/sec. D.McClain, Sr. Scientist Raytheon Systems Co. Tucson, AZ Myron Brown <Myron.Brown@jhuapl.edu> wrote in message news:87engh$t1a$1@houston.jhuapl.edu... > Hi. Has anybody done any benchmarking of IDL's > FFT routines? They seem pretty fast, actually. I'm > wondering how they compare to efficient C code. > Perhaps someone has looked at fftpack or other > efficient implementations of the FFT in C and compared > them? > > Anyone have any idea? > > Thanks. > > Myron Brown > Myron.Brown@jhuapl.edu > JHU Applied Physics Laboratory > >

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