DLAED5 used by sstedc. Solves the 2-by-2 secular equation.
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.
I is INTEGER The index of the eigenvalue to be computed. I = 1 or I = 2.
Z is DOUBLE PRECISION array, dimension (2) The components of the updating vector.
DELTA is DOUBLE PRECISION array, dimension (2) The vector DELTA contains the information necessary to construct the eigenvectors.
RHO is DOUBLE PRECISION The scalar in the symmetric updating formula.
DLAM is DOUBLE PRECISION The computed lambda_I, the I-th updated eigenvalue.
Univ. of California Berkeley
Univ. of Colorado Denver
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