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dlasd5 examples
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Man Page Details
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NAME
       DLASD5  -  compute 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  The diagonal entries in the array D are assumed to
       satisfy   0 <= D(i) < D(j) for i < j

SYNOPSIS
       SUBROUTINE DLASD5( I, D, Z, DELTA, RHO, DSIGMA, WORK )

           INTEGER        I

           DOUBLE         PRECISION DSIGMA, RHO

           DOUBLE         PRECISION D( 2 ), DELTA( 2 ), WORK( 2 ), Z( 2 )

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

       We  also  assume RHO > 0 and that the Euclidean norm of the vector Z is
       one.


ARGUMENTS
       I      (input) INTEGER
              The index of the eigenvalue to be computed.  I = 1 or I = 2.

       D      (input) DOUBLE PRECISION array, dimension ( 2 )
              The original eigenvalues.  We assume 0 <= D(1) < D(2).

       Z      (input) DOUBLE PRECISION array, dimension ( 2 )
              The components of the updating vector.

       DELTA  (output) 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 eigen-
              vectors.

       RHO    (input) DOUBLE PRECISION
              The scalar in the symmetric updating formula.

              DSIGMA (output) DOUBLE PRECISION The computed sigma_I, the  I-th
              updated eigenvalue.

       WORK   (workspace) DOUBLE PRECISION array, dimension ( 2 )
              WORK contains (D(j) + sigma_I) in its  j-th component.

