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slasd5.f(3) | LAPACK | slasd5.f(3) |
NAME¶
slasd5.f -SYNOPSIS¶
Functions/Subroutines¶
subroutine slasd5 (I, D, Z, DELTA, RHO, DSIGMA, WORK)
Function/Subroutine Documentation¶
subroutine slasd5 (integerI, real, dimension( 2 )D, real, dimension( 2 )Z, real, dimension( 2 )DELTA, realRHO, realDSIGMA, real, dimension( 2 )WORK)¶
SLASD5 computes the square root of the i-th eigenvalue of a positive symmetric rank-one modification of a 2-by-2 diagonal matrix. Used by sbdsdc. Purpose:This subroutine computes the square root of the I-th eigenvalue of a positive symmetric rank-one modification of a 2-by-2 diagonal matrix diag( D ) * diag( D ) + RHO * Z * transpose(Z) . The diagonal entries in the array D are assumed to satisfy 0 <= D(i) < D(j) for i < j . We also assume RHO > 0 and that the Euclidean norm of the vector Z is one.
I
Author:
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 0 <= D(1) < D(2).Z
Z is REAL array, dimension (2) The components of the updating vector.DELTA
DELTA is REAL array, dimension (2) Contains (D(j) - sigma_I) in its j-th component. The vector DELTA contains the information necessary to construct the eigenvectors.RHO
RHO is REAL The scalar in the symmetric updating formula.DSIGMA
DSIGMA is REAL The computed sigma_I, the I-th updated eigenvalue.WORK
WORK is REAL array, dimension (2) WORK contains (D(j) + sigma_I) in its j-th component.
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
September 2012
Contributors:
Ren-Cang Li, Computer Science Division, University of
California at Berkeley, USA
Definition at line 117 of file slasd5.f.
Author¶
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