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slaed5.f(3) LAPACK slaed5.f(3)

NAME

slaed5.f -

SYNOPSIS

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 (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.
Parameters:
I 
          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.
Date:
September 2012
Contributors:
Ren-Cang Li, Computer Science Division, University of California at Berkeley, USA
Definition at line 109 of file slaed5.f.

Author

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