laed5 - laed5: D&C step: secular equation, 2x2

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subroutinedlaed5(integeri,doubleprecision,dimension(2)d,doubleprecision,dimension(2)z,doubleprecision,dimension(2)delta,doubleprecisionrho,doubleprecisiondlam)DLAED5 used by DSTEDC. Solves the 2-by-2 secular equation. Purpose: 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. ParametersI I is INTEGER The index of the eigenvalue to be computed. I = 1 or I = 2. D D is DOUBLE PRECISION array, dimension (2) The original eigenvalues. We assume D(1) < D(2). Z Z is DOUBLE PRECISION array, dimension (2) The components of the updating vector. DELTA DELTA is DOUBLE PRECISION array, dimension (2) The vector DELTA contains the information necessary to construct the eigenvectors. RHO RHO is DOUBLE PRECISION The scalar in the symmetric updating formula. DLAM DLAM is DOUBLE PRECISION The computed lambda_I, the I-th updated eigenvalue. Author Univ. of Tennessee Univ. of California Berkeley Univ. of Colorado Denver NAG Ltd. Contributors: Ren-Cang Li, Computer Science Division, University of California at Berkeley, USA subroutineslaed5(integeri,real,dimension(2)d,real,dimension(2)z,real,dimension(2)delta,realrho,realdlam)SLAED5 used by SSTEDC. Solves the 2-by-2 secular equation. Purpose: 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. ParametersI I is INTEGER The index of the eigenvalue to be computed. I = 1 or I = 2. D D is REAL array, dimension (2) The original eigenvalues. We assume D(1) < D(2). Z Z is REAL array, dimension (2) The components of the updating vector. DELTA DELTA is REAL array, dimension (2) The vector DELTA contains the information necessary to construct the eigenvectors. RHO RHO is REAL The scalar in the symmetric updating formula. DLAM DLAM is REAL The computed lambda_I, the I-th updated eigenvalue. Author Univ. of Tennessee Univ. of California Berkeley Univ. of Colorado Denver NAG Ltd. Contributors: Ren-Cang Li, Computer Science Division, University of California at Berkeley, USA

laed5 - laed5: D&C step: secular equation, 2x2

Functions subroutine dlaed5 (i, d, z, delta, rho, dlam) DLAED5 used by DSTEDC. Solves the 2-by-2 secular equation. subroutine slaed5 (i, d, z, delta, rho, dlam) SLAED5 used by SSTEDC. Solves the 2-by-2 secular equation.