LAPACK  3.4.2
LAPACK: Linear Algebra PACKage
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slaed5.f File Reference

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Functions/Subroutines

subroutine slaed5 (I, D, Z, DELTA, RHO, DLAM)
 SLAED5 used by sstedc. Solves the 2-by-2 secular equation.

Function/Subroutine Documentation

subroutine slaed5 ( integer  I,
real, dimension( 2 )  D,
real, dimension( 2 )  Z,
real, dimension( 2 )  DELTA,
real  RHO,
real  DLAM 
)

SLAED5 used by sstedc. Solves the 2-by-2 secular equation.

Download SLAED5 + dependencies [TGZ] [ZIP] [TXT]
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.
Parameters:
[in]I
          I is INTEGER
         The index of the eigenvalue to be computed.  I = 1 or I = 2.
[in]D
          D is REAL array, dimension (2)
         The original eigenvalues.  We assume D(1) < D(2).
[in]Z
          Z is REAL array, dimension (2)
         The components of the updating vector.
[out]DELTA
          DELTA is REAL array, dimension (2)
         The vector DELTA contains the information necessary
         to construct the eigenvectors.
[in]RHO
          RHO is REAL
         The scalar in the symmetric updating formula.
[out]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.
Date:
September 2012
Contributors:
Ren-Cang Li, Computer Science Division, University of California at Berkeley, USA

Definition at line 109 of file slaed5.f.

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