dlasd5.f (3) - Linux Manuals
NAME
dlasd5.f -
SYNOPSIS
Functions/Subroutines
subroutine dlasd5 (I, D, Z, DELTA, RHO, DSIGMA, WORK)
DLASD5 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.
Function/Subroutine Documentation
subroutine dlasd5 (integerI, double precision, dimension( 2 )D, double precision, dimension( 2 )Z, double precision, dimension( 2 )DELTA, double precisionRHO, double precisionDSIGMA, double precision, dimension( 2 )WORK)
DLASD5 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.
Parameters:
-
I
I is INTEGER The index of the eigenvalue to be computed. I = 1 or I = 2.
DD is DOUBLE PRECISION array, dimension ( 2 ) The original eigenvalues. We assume 0 <= D(1) < D(2).
ZZ is DOUBLE PRECISION array, dimension ( 2 ) The components of the updating vector.
DELTADELTA is DOUBLE PRECISION array, dimension ( 2 ) Contains (D(j) - sigma_I) in its j-th component. The vector DELTA contains the information necessary to construct the eigenvectors.
RHORHO is DOUBLE PRECISION The scalar in the symmetric updating formula.
DSIGMADSIGMA is DOUBLE PRECISION The computed sigma_I, the I-th updated eigenvalue.
WORKWORK is DOUBLE PRECISION array, dimension ( 2 ) WORK contains (D(j) + sigma_I) in its j-th component.
Author:
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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 dlasd5.f.
Author
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