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Expressions régulières,
Syntaxe et mise en oeuvre :
GNU/Linux |
CentOS 4.8 |
i386 |
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dlasq1(l) |
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DLASQ1 - compute the singular values of a real N-by-N bidiagonal matrix with diagonal D and off-diagonal E
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SUBROUTINE DLASQ1( |
N, D, E, WORK, INFO ) |
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INTEGER |
INFO, N |
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DOUBLE |
PRECISION D( * ), E( * ), WORK( * ) |
DLASQ1 computes the singular values of a real N-by-N bidiagonal matrix with diagonal D and off-diagonal E. The singular values are computed to high relative accuracy, in the absence of denormalization, underflow and overflow. The algorithm was first presented in
"Accurate singular values and differential qd algorithms" by K. V. Fernando and B. N. Parlett, Numer. Math., Vol-67, No. 2, pp. 191-230, 1994,
and the present implementation is described in "An implementation of the dqds Algorithm (Positive Case)", LAPACK Working Note.
N (input) INTEGER
The number of rows and columns in the matrix. N >= 0.
D (input/output) DOUBLE PRECISION array, dimension (N)
On entry, D contains the diagonal elements of the bidiagonal matrix whose SVD is desired. On normal exit, D contains the singular values in decreasing order.
E (input/output) DOUBLE PRECISION array, dimension (N)
On entry, elements E(1:N-1) contain the off-diagonal elements of the bidiagonal matrix whose SVD is desired. On exit, E is overwritten.
WORK (workspace) DOUBLE
PRECISION array, dimension (4*N)
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
> 0: the algorithm failed = 1, a split was marked by a
positive value in E = 2, current block of Z not diagonalized
after 30*N iterations (in inner while loop) = 3, termination
criterion of outer while loop not met (program created more
than N unreduced blocks)
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dlasq1(l) | |