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From: Marcelo Marazzi <mREMOVEmaALLraCAPITALSzzi@mathworks.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: nonnegative Ax=b lsq for large, sparse A.
Date: Fri, 26 Jun 2009 13:47:32 -0400
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Tom,

lsqnonneg was upgraded in version R2008b; it now uses sparse linear algebra if the
matrix is sparse (it uses "\", backslash).

R2008b Release notes:
http://www.mathworks.com/access/helpdesk/help/techdoc/rn/brqyzsl-1.html
(See "Upgrades to lsqnonneg".)

-Marcelo

Thomas Clark wrote:
> Hello all,
> 
> I have a large, sparse, rectangular (overdetermined) matrix A.
> 
> I'm solving Ax = b, where all elements of A, x and b are nonnegative.
> 
> I thought at first that lsqnonneg would be my ideal function, however, I hadn't realised that it is not useful for large sparse matrices (creates a full matrix the same size as A).
> 
> Does anyone know of an alternative for lsqnonneg which may be used with a large, sparse coefficients matrix?
> 
> A sample of the problem (.mat file containing A and b) can be found in:
> http://www2.eng.cam.ac.uk/~thc29/lsqnonneg_sparse/
> 
> Tim Davis, if you happen across this, you may enjoy the sparsity pattern (it's for a tomographic reconstruction of a particle field in fluid flow).
> 
> Thanks all, and kind regards
> 
> Tom Clark