dlaeda(3S)

NAME
     DLAEDA - 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 DLAEDA( 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( * )

         DOUBLE         PRECISION GIVNUM( 2, * ), Q( * ), Z( * ), ZTEMP( * )

IMPLEMENTATION
     These routines are part of the SCSL Scientific Library and can be loaded
     using either the -lscs or the -lscs_mp option.  The -lscs_mp option
     directs the linker to use the multi-processor version of the library.

     When linking to SCSL with -lscs or -lscs_mp, the default integer size is
     4 bytes (32 bits). Another version of SCSL is available in which integers
     are 8 bytes (64 bits).  This version allows the user access to larger
     memory sizes and helps when porting legacy Cray codes.  It can be loaded
     by using the -lscs_i8 option or the -lscs_i8_mp option. A program may use
     only one of the two versions; 4-byte integer and 8-byte integer library
     calls cannot be mixed.

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

     Q      (input) DOUBLE PRECISION 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) DOUBLE PRECISION 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) DOUBLE PRECISION array, dimension (N)

     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


SEE ALSO
     INTRO_LAPACK(3S), INTRO_SCSL(3S)

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