SLAEDA (3lapack)

compute the Z vector corresponding to the merge step in the CURLVLth step of the merge process with TLVLS steps for the CURPBMth problem

SYNOPSIS

  SUBROUTINE SLAEDA( N, TLVLS, CURLVL, CURPBM, PRMPTR, PERM, GIVPTR, GIVCOL,
                     GIVNUM, Q, QPTR, Z, ZTEMP, INFO )

      INTEGER        CURLVL, CURPBM, INFO, N, TLVLS

      INTEGER        GIVCOL( 2, * ), GIVPTR( * ), PERM( * ), PRMPTR( * ),
                     QPTR( * )

      REAL           GIVNUM( 2, * ), Q( * ), Z( * ), ZTEMP( * )

PURPOSE

  SLAEDA computes the Z vector corresponding to the merge step in the
  CURLVLth step of the merge process with TLVLS steps for the CURPBMth
  problem.

ARGUMENTS

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

  TLVLS  (input) INTEGER
         The total number of merging levels in the overall divide and conquer
         tree.

         CURLVL (input) INTEGER The current level in the overall merge
         routine, 0 <= curlvl <= tlvls.

         CURPBM (input) INTEGER The current problem in the current level in
         the overall merge routine (counting from upper left to lower right).

         PRMPTR (input) INTEGER array, dimension (N lg N) Contains a list of
         pointers which indicate where in PERM a level's permutation is
         stored.  PRMPTR(i+1) - PRMPTR(i) indicates the size of the
         permutation and incidentally the size of the full, non-deflated
         problem.

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

         GIVPTR (input) INTEGER array, dimension (N lg N) Contains a list of
         pointers which indicate where in GIVCOL a level's Givens rotations
         are stored.  GIVPTR(i+1) - GIVPTR(i) indicates the number of Givens
         rotations.

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

         GIVNUM (input) REAL array, dimension (2, N lg N) Each number
         indicates the S value to be used in the corresponding Givens
         rotation.

  Q      (input) REAL array, dimension (N**2)
         Contains the square eigenblocks from previous levels, the starting
         positions for blocks are given by QPTR.

  QPTR   (input) INTEGER array, dimension (N+2)
         Contains a list of pointers which indicate where in Q an eigenblock
         is stored.  SQRT( QPTR(i+1) - QPTR(i) ) indicates the size of the
         block.

  Z      (output) REAL array, dimension (N)
         On output 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).

  ZTEMP  (workspace) REAL array, dimension (N)

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