SUBROUTINE DLAED5( I, D, Z, DELTA, RHO, DLAM ) INTEGER I DOUBLE PRECISION DLAM, RHO DOUBLE PRECISION D( 2 ), DELTA( 2 ), Z( 2 )
This subroutine computes the I-th eigenvalue of a symmetric rank-one modification of a 2-by-2 diagonal matrix We also assume RHO > 0 and that the Euclidean norm of the vector Z is one.
I (input) INTEGER The index of the eigenvalue to be computed. I = 1 or I = 2. D (input) DOUBLE PRECISION array, dimension (2) The original eigenvalues. We assume D(1) < D(2). Z (input) DOUBLE PRECISION array, dimension (2) The components of the updating vector. DELTA (output) DOUBLE PRECISION array, dimension (2) The vector DELTA contains the information necessary to construct the eigenvectors. RHO (input) DOUBLE PRECISION The scalar in the symmetric updating formula. DLAM (output) DOUBLE PRECISION The computed lambda_I, the I-th updated eigenvalue.