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*Subject*: Re: Blazing FAST!!! FFT's for IDL*From*: "David McClain" <dmcclain(at)azstarnet.com>*Date*: Thu, 30 Mar 2000 01:48:09 -0700*Newsgroups*: comp.lang.idl-pvwave*Organization*: Posted via Supernews, http://www.supernews.com*References*: <se64n3q1ni716@corp.supernews.com>*Xref*: news.doit.wisc.edu comp.lang.idl-pvwave:19086

Correction, the 2-D scaling should have been reported as 2n^2 log2 n. FYI, 75 MButterflys/sec corresponds to 128^2 images undergoing 2-D FFTs at roughly video frame rates.... - DM David McClain <dmcclain@azstarnet.com> wrote in message se64n3q1ni716@corp.supernews.com">news:se64n3q1ni716@corp.supernews.com... > I have some sources available on request to perform very, very, fast 1-D and > 2-D FFT's, forward and inverse, single and double precision. The speed > derives from a multithreaded manager written in C++ that calls on the Intel > Math Kernel implementation of 1-D FFT's. It is multithreaded because we > typically use dual and quad Pentium and Xeon machines. The manager code > sniffs out how many processors you have and spawns worker threads to match. > The arrays are then divied up between the different processor threads. The > IDL interface is quite simple, consisting of some data prep code and a bunch > of CALL_EXTERNAL's. > > We have been using this system for several years now. The Intel MKL expects > arrays in power of 2 size, unlike IDL, but it runs roughly 10-100 times > faster than IDL's routines the last time I checked about a year ago. It > properly scales as n*log2 n for 1-D and 2n*log2 n for 2-D n square arrays > (2-D arrays need not be square). IDL's routines scale quite dreadfully as > something on the order of n^2 (log2 n)^2 which implies some kind of tree > search on each Butterfly operation (???). Their routine is nice if you need > arbitrary array sizes, but power of 2 can always be used anyway: the > resulting spectrum is simply an interpolated spectrum at the intermediate > frequencies. > > On an old quad-Pentium II machine running at 200 MHz, the FFTX routines in > this package performed at roughly 75 MButterflys/sec. IDL ran about 3 > MButterflys/sec. > > If you are interested just drop me a line. The latest Intel MKL has been > sped up to roughly twice its former speed (the speed tests quoted were > performed on the old version of the MKL). It is available separately, and I > believe, still free, from Intel Corp. > > D. McClain > Sr. Scientist > Raytheon Systems Co. > Tucson, AZ > > >

**References**:**Blazing FAST!!! FFT's for IDL***From:*David McClain

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