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Re: multiplication by a diagonal matrix [message #40809 is a reply to message #40807]

Fri, 03 September 2004 07:42

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

lbusett@yahoo.it (Lorenzo Busetto) writes:

> Hi all,
>
> I have the following problem: given a matrix A(n,m) and a vector of
> weighting factors w(n), i need to multiply each row of the matrix
> A(i,*)by the corresponding weighting factor w(i).

It sounds like you want to use a FOR loop. When N is small, the
number of loop iterations is small, so it will be fast. When N is
large, the number of loop iterations is larger too, but you also get
more done per iteration (N multiplies per iteration), plus you save
N*(N-1) elements of memory compared to the full matrix approach.

Craig

Good luck,
Craig

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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@REMOVEcow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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[Message index]

		Re: multiplication by a diagonal matrix By: gnarloo on Fri, 03 September 2004 11:03
		Re: multiplication by a diagonal matrix By: JD Smith on Fri, 03 September 2004 08:01
		Re: multiplication by a diagonal matrix By: Craig Markwardt on Fri, 03 September 2004 07:42
		Re: multiplication by a diagonal matrix By: Paolo Grigis on Fri, 03 September 2004 05:32
		Re: multiplication by a diagonal matrix By: lbusett on Wed, 08 September 2004 05:50

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