ZLAED8(l)								 )								 ZLAED8(l)

NAME

       ZLAED8 - merge the two sets of eigenvalues together into a single sorted set

SYNOPSIS

       SUBROUTINE ZLAED8( K, N, QSIZ, Q, LDQ, D, RHO, CUTPNT, Z, DLAMDA, Q2, LDQ2, W, INDXP, INDX, INDXQ, PERM, GIVPTR, GIVCOL, GIVNUM, INFO )

	   INTEGER	  CUTPNT, GIVPTR, INFO, K, LDQ, LDQ2, N, QSIZ

	   DOUBLE	  PRECISION RHO

	   INTEGER	  GIVCOL( 2, * ), INDX( * ), INDXP( * ), INDXQ( * ), PERM( * )

	   DOUBLE	  PRECISION D( * ), DLAMDA( * ), GIVNUM( 2, * ), W( * ), Z( * )

	   COMPLEX*16	  Q( LDQ, * ), Q2( LDQ2, * )

PURPOSE

       ZLAED8  merges  the  two sets of eigenvalues together into a single sorted set. Then it tries to deflate the size of the problem. There are
       two ways in which deflation can occur:  when two or more eigenvalues are close together or if there is a tiny element in the Z vector.  For
       each such occurrence the order of the related secular equation problem is reduced by one.

ARGUMENTS

       K      (output) INTEGER
	      Contains the number of non-deflated eigenvalues.	This is the order of the related secular equation.

       N      (input) INTEGER
	      The dimension of the symmetric tridiagonal matrix.  N >= 0.

       QSIZ   (input) INTEGER
	      The dimension of the unitary matrix used to reduce the dense or band matrix to tridiagonal form.	QSIZ >= N if ICOMPQ = 1.

       Q      (input/output) COMPLEX*16 array, dimension (LDQ,N)
	      On  entry,  Q  contains  the eigenvectors of the partially solved system which has been previously updated in matrix multiplies with
	      other partially solved eigensystems.  On exit, Q contains the trailing (N-K) updated eigenvectors (those which were deflated) in its
	      last N-K columns.

       LDQ    (input) INTEGER
	      The leading dimension of the array Q.  LDQ >= max( 1, N ).

       D      (input/output) DOUBLE PRECISION array, dimension (N)
	      On  entry,  D contains the eigenvalues of the two submatrices to be combined.  On exit, D contains the trailing (N-K) updated eigen-
	      values (those which were deflated) sorted into increasing order.

       RHO    (input/output) DOUBLE PRECISION
	      Contains the off diagonal element associated with the rank-1 cut which originally split the two  submatrices  which  are	now  being
	      recombined. RHO is modified during the computation to the value required by DLAED3.

	      CUTPNT (input) INTEGER Contains the location of the last eigenvalue in the leading sub-matrix.  MIN(1,N) <= CUTPNT <= N.

       Z      (input) DOUBLE PRECISION array, dimension (N)
	      On  input this vector contains the updating vector (the last row of the first sub-eigenvector matrix and the first row of the second
	      sub-eigenvector matrix).	The contents of Z are destroyed during the updating process.

	      DLAMDA (output) DOUBLE PRECISION array, dimension (N) Contains a copy of the first K eigenvalues which will be  used  by	DLAED3	to
	      form the secular equation.

       Q2     (output) COMPLEX*16 array, dimension (LDQ2,N)
	      If  ICOMPQ  =  0,  Q2  is  not referenced.  Otherwise, Contains a copy of the first K eigenvectors which will be used by DLAED7 in a
	      matrix multiply (DGEMM) to update the new eigenvectors.

       LDQ2   (input) INTEGER
	      The leading dimension of the array Q2.  LDQ2 >= max( 1, N ).

       W      (output) DOUBLE PRECISION array, dimension (N)
	      This will hold the first k values of the final deflation-altered z-vector and will be passed to DLAED3.

       INDXP  (workspace) INTEGER array, dimension (N)
	      This will contain the permutation used to place deflated values of D at the end of the array. On output INDXP(1:K)
	      points to the nondeflated D-values and INDXP(K+1:N) points to the deflated eigenvalues.

       INDX   (workspace) INTEGER array, dimension (N)
	      This will contain the permutation used to sort the contents of D into ascending order.

       INDXQ  (input) INTEGER array, dimension (N)
	      This contains the permutation which separately sorts the two sub-problems in D into ascending order.  Note that elements in the sec-
	      ond half of this permutation must first have CUTPNT added to their values in order to be accurate.

       PERM   (output) INTEGER array, dimension (N)
	      Contains the permutations (from deflation and sorting) to be applied to each eigenblock.

	      GIVPTR (output) INTEGER Contains the number of Givens rotations which took place in this subproblem.

	      GIVCOL (output) INTEGER array, dimension (2, N) Each pair of numbers indicates a pair of columns to take place in a Givens rotation.

	      GIVNUM  (output)	DOUBLE	PRECISION array, dimension (2, N) Each number indicates the S value to be used in the corresponding Givens
	      rotation.

       INFO   (output) INTEGER
	      = 0:  successful exit.
	      < 0:  if INFO = -i, the i-th argument had an illegal value.

LAPACK version 3.0						   15 June 2000 							 ZLAED8(l)