bugGNU Scientific Library - Bugs: bug #52321, gsl_linalg_bidiag_unpack2...


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bug #52321: gsl_linalg_bidiag_unpack2 functioan has wrong householder transform call for V in GSL1.8

Submitted by:  Patrick Alken <psa>
Submitted on:  Wed 01 Nov 2017 09:05:27 AM UTC  
Category:  Runtime error Severity:  3 - Normal
Operating System:  Status:  None
Assigned to:  None Open/Closed:  Open

Wed 01 Nov 2017 09:05:27 AM UTC, original submission:

from actionafterthought =at= gmail =dot= com


This bug might have been fixed. Since it is in GSL 1.8 source. And it is noticed that the wrong householder transform
Function call is made for a row vector from V (see below code). And the correct function call for highlighted line is
supposed to be:

gsl_linalg_householder_mh (ti, &h.vector, &m.matrix);

gsl_linalg_bidiag_unpack2 (gsl_matrix * A,
gsl_vector * tau_U,
gsl_vector * tau_V,
gsl_matrix * V)

/* Initialize V to the identity */

gsl_matrix_set_identity (V);

for (i = N - 1; i > 0 && i--;)
/* Householder row transformation to accumulate V */
gsl_vector_const_view r = gsl_matrix_const_row (A, i);
gsl_vector_const_view h =
gsl_vector_const_subvector (&r.vector, i + 1, N - (i+1));

double ti = gsl_vector_get (tau_V, i);

gsl_matrix_view m =
gsl_matrix_submatrix (V, i + 1, i + 1, N-(i+1), N-(i+1));

gsl_linalg_householder_hm (ti, &h.vector, &m.matrix);

Patrick Alken <psa>
Project Administrator


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