[comp.sources.wanted] Need fft-based autocovariance func.

john@prism.UUCP (12/24/87)

I am working on a general purpose program to manipulate physiological 
time series data with the IBM pc in Lattice c.  I need to calculate auto- and 
cross-covariance functions.  I know from several texts that there 
are ways of greatly speeding up covariance functions using the FFT.  
The problem is, none of these sources say in enough detail, and in 
simple enough terms, how to do this.  I even have a working fft 
function.  I just don't have enough math/engineering background/ability 
to put it all together. 

Is there anyone out there who could give me an algorithm or source for 
doing this?  
                                         
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JOHN DOWD	john@mirror.TMC.COM
{mit-eddie, ihnp4, harvard!wjh12, cca, cbosgd, seismo}!mirror!john
Mirror Systems	Cambridge, MA  02140