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    1: *> \brief \b DLASDT creates a tree of subproblems for bidiagonal divide and conquer. Used by sbdsdc.
    2: *
    3: *  =========== DOCUMENTATION ===========
    4: *
    5: * Online html documentation available at
    6: *            http://www.netlib.org/lapack/explore-html/
    7: *
    8: *> \htmlonly
    9: *> Download DLASDT + dependencies
   10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlasdt.f">
   11: *> [TGZ]</a>
   12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlasdt.f">
   13: *> [ZIP]</a>
   14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlasdt.f">
   15: *> [TXT]</a>
   16: *> \endhtmlonly
   17: *
   18: *  Definition:
   19: *  ===========
   20: *
   21: *       SUBROUTINE DLASDT( N, LVL, ND, INODE, NDIML, NDIMR, MSUB )
   22: *
   23: *       .. Scalar Arguments ..
   24: *       INTEGER            LVL, MSUB, N, ND
   25: *       ..
   26: *       .. Array Arguments ..
   27: *       INTEGER            INODE( * ), NDIML( * ), NDIMR( * )
   28: *       ..
   29: *
   30: *
   31: *> \par Purpose:
   32: *  =============
   33: *>
   34: *> \verbatim
   35: *>
   36: *> DLASDT creates a tree of subproblems for bidiagonal divide and
   37: *> conquer.
   38: *> \endverbatim
   39: *
   40: *  Arguments:
   41: *  ==========
   42: *
   43: *> \param[in] N
   44: *> \verbatim
   45: *>          N is INTEGER
   46: *>          On entry, the number of diagonal elements of the
   47: *>          bidiagonal matrix.
   48: *> \endverbatim
   49: *>
   50: *> \param[out] LVL
   51: *> \verbatim
   52: *>          LVL is INTEGER
   53: *>          On exit, the number of levels on the computation tree.
   54: *> \endverbatim
   55: *>
   56: *> \param[out] ND
   57: *> \verbatim
   58: *>          ND is INTEGER
   59: *>          On exit, the number of nodes on the tree.
   60: *> \endverbatim
   61: *>
   62: *> \param[out] INODE
   63: *> \verbatim
   64: *>          INODE is INTEGER array, dimension ( N )
   65: *>          On exit, centers of subproblems.
   66: *> \endverbatim
   67: *>
   68: *> \param[out] NDIML
   69: *> \verbatim
   70: *>          NDIML is INTEGER array, dimension ( N )
   71: *>          On exit, row dimensions of left children.
   72: *> \endverbatim
   73: *>
   74: *> \param[out] NDIMR
   75: *> \verbatim
   76: *>          NDIMR is INTEGER array, dimension ( N )
   77: *>          On exit, row dimensions of right children.
   78: *> \endverbatim
   79: *>
   80: *> \param[in] MSUB
   81: *> \verbatim
   82: *>          MSUB is INTEGER
   83: *>          On entry, the maximum row dimension each subproblem at the
   84: *>          bottom of the tree can be of.
   85: *> \endverbatim
   86: *
   87: *  Authors:
   88: *  ========
   89: *
   90: *> \author Univ. of Tennessee
   91: *> \author Univ. of California Berkeley
   92: *> \author Univ. of Colorado Denver
   93: *> \author NAG Ltd.
   94: *
   95: *> \ingroup OTHERauxiliary
   96: *
   97: *> \par Contributors:
   98: *  ==================
   99: *>
  100: *>     Ming Gu and Huan Ren, Computer Science Division, University of
  101: *>     California at Berkeley, USA
  102: *>
  103: *  =====================================================================
  104:       SUBROUTINE DLASDT( N, LVL, ND, INODE, NDIML, NDIMR, MSUB )
  105: *
  106: *  -- LAPACK auxiliary routine --
  107: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
  108: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
  109: *
  110: *     .. Scalar Arguments ..
  111:       INTEGER            LVL, MSUB, N, ND
  112: *     ..
  113: *     .. Array Arguments ..
  114:       INTEGER            INODE( * ), NDIML( * ), NDIMR( * )
  115: *     ..
  116: *
  117: *  =====================================================================
  118: *
  119: *     .. Parameters ..
  120:       DOUBLE PRECISION   TWO
  121:       PARAMETER          ( TWO = 2.0D+0 )
  122: *     ..
  123: *     .. Local Scalars ..
  124:       INTEGER            I, IL, IR, LLST, MAXN, NCRNT, NLVL
  125:       DOUBLE PRECISION   TEMP
  126: *     ..
  127: *     .. Intrinsic Functions ..
  128:       INTRINSIC          DBLE, INT, LOG, MAX
  129: *     ..
  130: *     .. Executable Statements ..
  131: *
  132: *     Find the number of levels on the tree.
  133: *
  134:       MAXN = MAX( 1, N )
  135:       TEMP = LOG( DBLE( MAXN ) / DBLE( MSUB+1 ) ) / LOG( TWO )
  136:       LVL = INT( TEMP ) + 1
  137: *
  138:       I = N / 2
  139:       INODE( 1 ) = I + 1
  140:       NDIML( 1 ) = I
  141:       NDIMR( 1 ) = N - I - 1
  142:       IL = 0
  143:       IR = 1
  144:       LLST = 1
  145:       DO 20 NLVL = 1, LVL - 1
  146: *
  147: *        Constructing the tree at (NLVL+1)-st level. The number of
  148: *        nodes created on this level is LLST * 2.
  149: *
  150:          DO 10 I = 0, LLST - 1
  151:             IL = IL + 2
  152:             IR = IR + 2
  153:             NCRNT = LLST + I
  154:             NDIML( IL ) = NDIML( NCRNT ) / 2
  155:             NDIMR( IL ) = NDIML( NCRNT ) - NDIML( IL ) - 1
  156:             INODE( IL ) = INODE( NCRNT ) - NDIMR( IL ) - 1
  157:             NDIML( IR ) = NDIMR( NCRNT ) / 2
  158:             NDIMR( IR ) = NDIMR( NCRNT ) - NDIML( IR ) - 1
  159:             INODE( IR ) = INODE( NCRNT ) + NDIML( IR ) + 1
  160:    10    CONTINUE
  161:          LLST = LLST*2
  162:    20 CONTINUE
  163:       ND = LLST*2 - 1
  164: *
  165:       RETURN
  166: *
  167: *     End of DLASDT
  168: *
  169:       END