SLAED2(l)								 )								 SLAED2(l)

NAME

       SLAED2 - merge the two sets of eigenvalues together into a single sorted set

SYNOPSIS

       SUBROUTINE SLAED2( K, N, N1, D, Q, LDQ, INDXQ, RHO, Z, DLAMDA, W, Q2, INDX, INDXC, INDXP, COLTYP, INFO )

	   INTEGER	  INFO, K, LDQ, N, N1

	   REAL 	  RHO

	   INTEGER	  COLTYP( * ), INDX( * ), INDXC( * ), INDXP( * ), INDXQ( * )

	   REAL 	  D( * ), DLAMDA( * ), Q( LDQ, * ), Q2( * ), W( * ), Z( * )

PURPOSE

       SLAED2  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 entry in the Z  vector.   For
       each such occurrence the order of the related secular equation problem is reduced by one.

ARGUMENTS

       K      (output) INTEGER
	      The number of non-deflated eigenvalues, and the order of the related secular equation. 0 <= K <=N.

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

       N1     (input) INTEGER
	      The location of the last eigenvalue in the leading sub-matrix.  min(1,N) <= N1 <= N/2.

       D      (input/output) REAL 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.

       Q      (input/output) REAL array, dimension (LDQ, N)
	      On entry, Q contains the eigenvectors of two submatrices in the two square blocks with corners at (1,1), (N1,N1) and  (N1+1,  N1+1),
	      (N,N).  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).

       INDXQ  (input/output) INTEGER array, dimension (N)
	      The  permutation	which  separately  sorts the two sub-problems in D into ascending order.  Note that elements in the second half of
	      this permutation must first have N1 added to their values. Destroyed on exit.

       RHO    (input/output) REAL
	      On entry, the off-diagonal element associated with the rank-1 cut which originally split the two submatrices  which  are	now  being
	      recombined.  On exit, RHO has been modified to the value required by SLAED3.

       Z      (input) REAL array, dimension (N)
	      On  entry,  Z  contains  the  updating vector (the last row of the first sub-eigenvector matrix and the first row of the second sub-
	      eigenvector matrix).  On exit, the contents of Z have been destroyed by the updating process.

	      DLAMDA (output) REAL array, dimension (N) A copy of the first K eigenvalues which will be used by SLAED3 to form the  secular  equa-
	      tion.

       W      (output) REAL array, dimension (N)
	      The first k values of the final deflation-altered z-vector which will be passed to SLAED3.

       Q2     (output) REAL array, dimension (N1**2+(N-N1)**2)
	      A copy of the first K eigenvectors which will be used by SLAED3 in a matrix multiply (SGEMM) to solve for the new eigenvectors.

       INDX   (workspace) INTEGER array, dimension (N)
	      The permutation used to sort the contents of DLAMDA into ascending order.

       INDXC  (output) INTEGER array, dimension (N)
	      The  permutation used to arrange the columns of the deflated Q matrix into three groups:	the first group contains non-zero elements
	      only at and above N1, the second contains non-zero elements only below N1, and the third is dense.

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

	      COLTYP (workspace/output) INTEGER array, dimension (N) During execution, a label which will indicate which of the following types  a
	      column in the Q2 matrix is:
	      1 : non-zero in the upper half only;
	      2 : dense;
	      3 : non-zero in the lower half only;
	      4 : deflated.  On exit, COLTYP(i) is the number of columns of type i, for i=1 to 4 only.

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

FURTHER DETAILS

       Based on contributions by
	  Jeff Rutter, Computer Science Division, University of California
	  at Berkeley, USA
       Modified by Francoise Tisseur, University of Tennessee.

LAPACK version 3.0						   15 June 2000 							 SLAED2(l)