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From: allanh@netcom.COM (Allan N. Hessenflow)
Newsgroups: comp.dsp
Subject: factoring matrices question
Message-ID: <1991Apr8.200939.5533@netcom.COM>
Date: 8 Apr 91 20:09:39 GMT
Organization: Netcom - Online Communication Services  UNIX System {408 241-9760 guest}
Lines: 16

I've been told that there's a way to factor the following matrix so that,
when it's multiplied by a column vector, the total number of multiplications
are reduced (2:1?) at the expense of some additions.  However, I can't see
how.  Any insights would be appreciated.

 c3 -c5  c1 -c7
 c5  c3 -c7 -c1
-c7  c1  c3  c5
 c1  c7 -c5  c3

where cn=cos(n*pi/16).

allan

-- 
Allan N. Hessenflow   {apple|claris}!netcom!allanh    allanh@netcom.com