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LAPACK
3.7.0
LAPACK: Linear Algebra PACKage
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subroutine dlaed5 | ( | integer | I, |
double precision, dimension( 2 ) | D, | ||
double precision, dimension( 2 ) | Z, | ||
double precision, dimension( 2 ) | DELTA, | ||
double precision | RHO, | ||
double precision | DLAM | ||
) |
DLAED5 used by sstedc. Solves the 2-by-2 secular equation.
Download DLAED5 + dependencies [TGZ] [ZIP] [TXT]
This subroutine computes the I-th eigenvalue of a symmetric rank-one modification of a 2-by-2 diagonal matrix diag( D ) + RHO * Z * transpose(Z) . The diagonal elements in the array D are assumed to satisfy D(i) < D(j) for i < j . We also assume RHO > 0 and that the Euclidean norm of the vector Z is one.
[in] | I | I is INTEGER The index of the eigenvalue to be computed. I = 1 or I = 2. |
[in] | D | D is DOUBLE PRECISION array, dimension (2) The original eigenvalues. We assume D(1) < D(2). |
[in] | Z | Z is DOUBLE PRECISION array, dimension (2) The components of the updating vector. |
[out] | DELTA | DELTA is DOUBLE PRECISION array, dimension (2) The vector DELTA contains the information necessary to construct the eigenvectors. |
[in] | RHO | RHO is DOUBLE PRECISION The scalar in the symmetric updating formula. |
[out] | DLAM | DLAM is DOUBLE PRECISION The computed lambda_I, the I-th updated eigenvalue. |
Definition at line 110 of file dlaed5.f.