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## Re: [Help-gsl] Re: QR Decomposition for a matrix with complex values

**From**: |
Brian Gough |

**Subject**: |
Re: [Help-gsl] Re: QR Decomposition for a matrix with complex values |

**Date**: |
Thu, 31 Jan 2008 18:02:37 +0000 |

**User-agent**: |
Wanderlust/2.14.0 (Africa) Emacs/22.1 Mule/5.0 (SAKAKI) |

At Tue, 29 Jan 2008 11:46:17 +0000,
Jonny Taylor wrote:
>* With that taken into account, I've got it working. Source file is *
>* attached in case it is of use to anybody. I have not included *
>* equivalents of some of the functions in qr.c because I did not test *
>* them since I don't need them. I have no idea whether it's more *
>* "correct" to store tau or its conjugate in the tau vector; I have *
>* chosen to store the conjugate.*
It's best to follow LAPACK (routine CGEQRF) which stores tau.
The matrix Q is represented as a product of elementary reflectors
Q = H(1) H(2) . . . H(k), where k = min(m,n).
Each H(i) has the form
H(i) = I - tau * v * v'
where tau is a complex scalar, and v is a complex vector with v(1:i-1)
= 0 and v(i) = 1; v(i+1:m) is stored on exit in A(i+1:m,i), and tau in
TAU(i).