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Re: multiplication by a diagonal matrix [message #40806]

Fri, 03 September 2004 11:03

gnarloo
Messages: 14
Registered: June 2004

Junior Member

guarda,
if you build a matrix with the n vectors (the weights)
and then you write

w*a
idl performs the multiplication element by element
lascia stare diag_matrix che complica solo le cose, idl supporta
le stesse notationi tra matrici e numeri e se scrivi w*a
ti fa direttamente il conto che vuoi tu.

but first you have to build the matrix out of the set of weight vectors

ciao

> 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).
>
> I know that I can simply "transform" the w vector into a diagonal
> matrix with diag_matrix and then multiply it with A (e.g.: result =
> A##diag_matrix(w)), but for large values of n this solution is very
> slow.
>
> Can anybody suggest me a faster approach to solve this problem ?
>
> Thanks in advance for the help,
>
> Lorenzo Busetto
>
> Remote Sensing Lab.
> University of Milano-Bicocca.

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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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