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From: plonski@aero.aero.org (Mike Plonski)
Newsgroups: comp.lang.idl-pvwave
Subject: Effecient way to multiply every col in matrix by a col vector??
Message-ID: <82772@aerospace.AERO.ORG>
Date: 31 Aug 90 19:11:50 GMT
Sender: news@aerospace.aero.org
Reply-To: plonski@aero.aero.org (Mike Plonski)
Organization: The Aerospace Corporation
Lines: 27

What is the most efficient way to multiply every col in a 2D array
(ncol x nrow) by a vector of length (ncol).

Example:

input array	vector		output array

a11 a12 a13	b1		a11b1 a12b1 a13b1
a21 a22 a23	b2		a21b2 a22b2 a23b2


I currently do this by looping over the cols:

	FOR i=0,ncol-1 DO c(i,*) = a(i,*) * b

Is there a more efficient way (w.r.t. computational speed) to do this?

I know I could replicate the column vector into a matrix (b # identity row)
and then do a ptwise matrix multiply, but my matrices can
be very large (1M elements) and I occasionally run out of swap
space.  I don't know if that would run any faster anyway.

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.   . .__.			       The opinions expressed herein are soley
|\./| !__!	 Michael Plonski       those of the author and do not represent
|   | |		"plonski@aero.org"     those of The Aerospace Corporation.
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