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MathGroup Archive 2005

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what kind of Pivoting does QRDecomposition use

  • To: mathgroup at smc.vnet.net
  • Subject: [mg54556] what kind of Pivoting does QRDecomposition use
  • From: "chiCong" <chicong.v at gmail.com>
  • Date: Tue, 22 Feb 2005 04:26:07 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Hello,

Can someone tell me what kind of Pivoting does QRDecomposition use when
I specify

[qq,rr,ee]=QRDecomposition[mm,Pivoting->True];

Mathematica document says that ee is a permutation "such that"

mm.ee == Transpose[qq].rr

but nothing more.

Especially, I want to have rr with decreasing diagonal elements (like
the way another system does it by the command "qr"). It seems that
Pivoting->True
doesn't work that way.

Regards, Cong


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