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Re: [Bug-gsl] linalg/bidiag.c

From: Brian Gough
Subject: Re: [Bug-gsl] linalg/bidiag.c
Date: Fri, 30 May 2003 15:35:26 +0100

Mario Pernici writes:
 >  As the example shows, the orthogonal matrix U obtained from
 > gsl_linalg_bidiag_unpack is a M x N matrix (linalg/bidiag.c line
 > 169) satisfying U^T U = I, but not U U^T = I, which is different
 > from the M x M orthogonal householder matrix U obtained from
 > sl_linalg_bidiag_decomp; V is the same in both cases; in both cases
 > one gets a bidiagonal matrix, but they differ (B has an extra row
 > of zeroes).
 >  In both cases B = U^T A V and A = U B V^T .  The
 >  gsl_linalg_bidiag_unpack results seem to be fine, but maybe it
 >  could be mentioned in the manual that the two U's and B's are
 >  different in the two functions.

Thanks -- now mentioned in the manual.  

The compact MxN form of the matrix is used for efficiency (important
for M>>N).


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