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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)
           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.

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.

       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 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.

       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 117 of file slasd5.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2                   Sat Nov 16 2013                    slasd5.f(3)

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