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From: "Bruno Luong" <b.luong@fogale.findmycountry>
Newsgroups: comp.soft-sys.matlab
Subject: Re: How to solve XA + B = 0?
Date: Fri, 3 Jul 2009 17:20:02 +0000 (UTC)
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"Tim Davis" <davis@cise.ufl.edu> wrote in message <h2ld57$3eg$1@fred.mathworks.com>...

> 
> You can use QR to get a min 2 norm solution of an underdetermined
> system, by factorizing A'.  That's what I do in the FACTORIZE package.
> x=A\b or b/A gives a basic solution to an underdetermined system,
> not a min 2norm solution.

Sorry it seems there is a miss understanding here, if B is *matrix*, X (solution of is underdetermined  system) is the matrix, and I have no idea how to select X that minimize the *global* spectral norm:

|X|_2 := max(X'*u)  for all u st |u|:=1
A*x = b

A: m x n; (m<n, A full rank)
B: m x p, (p>1)
X: n x p, (p>1)
u: n x 1, |u| = 1

I don't believe neither QR or even PINV could give the above. Or do I miss something?

Bruno