path: root/SRC/slalsa.f

*> \brief \b SLALSA computes the SVD of the coefficient matrix in compact form. Used by sgelsd.
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
*> \htmlonly
*> Download SLALSA + dependencies
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/slalsa.f">
*> [TGZ]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/slalsa.f">
*> [ZIP]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/slalsa.f">
*> [TXT]</a>
*> \endhtmlonly
*
*  Definition:
*  ===========
*
*       SUBROUTINE SLALSA( ICOMPQ, SMLSIZ, N, NRHS, B, LDB, BX, LDBX, U,
*                          LDU, VT, K, DIFL, DIFR, Z, POLES, GIVPTR,
*                          GIVCOL, LDGCOL, PERM, GIVNUM, C, S, WORK,
*                          IWORK, INFO )
*
*       .. Scalar Arguments ..
*       INTEGER            ICOMPQ, INFO, LDB, LDBX, LDGCOL, LDU, N, NRHS,
*      $                   SMLSIZ
*       ..
*       .. Array Arguments ..
*       INTEGER            GIVCOL( LDGCOL, * ), GIVPTR( * ), IWORK( * ),
*      $                   K( * ), PERM( LDGCOL, * )
*       REAL               B( LDB, * ), BX( LDBX, * ), C( * ),
*      $                   DIFL( LDU, * ), DIFR( LDU, * ),
*      $                   GIVNUM( LDU, * ), POLES( LDU, * ), S( * ),
*      $                   U( LDU, * ), VT( LDU, * ), WORK( * ),
*      $                   Z( LDU, * )
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> SLALSA is an itermediate step in solving the least squares problem
*> by computing the SVD of the coefficient matrix in compact form (The
*> singular vectors are computed as products of simple orthorgonal
*> matrices.).
*>
*> If ICOMPQ = 0, SLALSA applies the inverse of the left singular vector
*> matrix of an upper bidiagonal matrix to the right hand side; and if
*> ICOMPQ = 1, SLALSA applies the right singular vector matrix to the
*> right hand side. The singular vector matrices were generated in
*> compact form by SLALSA.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] ICOMPQ
*> \verbatim
*>          ICOMPQ is INTEGER
*>         Specifies whether the left or the right singular vector
*>         matrix is involved.
*>         = 0: Left singular vector matrix
*>         = 1: Right singular vector matrix
*> \endverbatim
*>
*> \param[in] SMLSIZ
*> \verbatim
*>          SMLSIZ is INTEGER
*>         The maximum size of the subproblems at the bottom of the
*>         computation tree.
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>         The row and column dimensions of the upper bidiagonal matrix.
*> \endverbatim
*>
*> \param[in] NRHS
*> \verbatim
*>          NRHS is INTEGER
*>         The number of columns of B and BX. NRHS must be at least 1.
*> \endverbatim
*>
*> \param[in,out] B
*> \verbatim
*>          B is REAL array, dimension ( LDB, NRHS )
*>         On input, B contains the right hand sides of the least
*>         squares problem in rows 1 through M.
*>         On output, B contains the solution X in rows 1 through N.
*> \endverbatim
*>
*> \param[in] LDB
*> \verbatim
*>          LDB is INTEGER
*>         The leading dimension of B in the calling subprogram.
*>         LDB must be at least max(1,MAX( M, N ) ).
*> \endverbatim
*>
*> \param[out] BX
*> \verbatim
*>          BX is REAL array, dimension ( LDBX, NRHS )
*>         On exit, the result of applying the left or right singular
*>         vector matrix to B.
*> \endverbatim
*>
*> \param[in] LDBX
*> \verbatim
*>          LDBX is INTEGER
*>         The leading dimension of BX.
*> \endverbatim
*>
*> \param[in] U
*> \verbatim
*>          U is REAL array, dimension ( LDU, SMLSIZ ).
*>         On entry, U contains the left singular vector matrices of all
*>         subproblems at the bottom level.
*> \endverbatim
*>
*> \param[in] LDU
*> \verbatim
*>          LDU is INTEGER, LDU = > N.
*>         The leading dimension of arrays U, VT, DIFL, DIFR,
*>         POLES, GIVNUM, and Z.
*> \endverbatim
*>
*> \param[in] VT
*> \verbatim
*>          VT is REAL array, dimension ( LDU, SMLSIZ+1 ).
*>         On entry, VT**T contains the right singular vector matrices of
*>         all subproblems at the bottom level.
*> \endverbatim
*>
*> \param[in] K
*> \verbatim
*>          K is INTEGER array, dimension ( N ).
*> \endverbatim
*>
*> \param[in] DIFL
*> \verbatim
*>          DIFL is REAL array, dimension ( LDU, NLVL ).
*>         where NLVL = INT(log_2 (N/(SMLSIZ+1))) + 1.
*> \endverbatim
*>
*> \param[in] DIFR
*> \verbatim
*>          DIFR is REAL array, dimension ( LDU, 2 * NLVL ).
*>         On entry, DIFL(*, I) and DIFR(*, 2 * I -1) record
*>         distances between singular values on the I-th level and
*>         singular values on the (I -1)-th level, and DIFR(*, 2 * I)
*>         record the normalizing factors of the right singular vectors
*>         matrices of subproblems on I-th level.
*> \endverbatim
*>
*> \param[in] Z
*> \verbatim
*>          Z is REAL array, dimension ( LDU, NLVL ).
*>         On entry, Z(1, I) contains the components of the deflation-
*>         adjusted updating row vector for subproblems on the I-th
*>         level.
*> \endverbatim
*>
*> \param[in] POLES
*> \verbatim
*>          POLES is REAL array, dimension ( LDU, 2 * NLVL ).
*>         On entry, POLES(*, 2 * I -1: 2 * I) contains the new and old
*>         singular values involved in the secular equations on the I-th
*>         level.
*> \endverbatim
*>
*> \param[in] GIVPTR
*> \verbatim
*>          GIVPTR is INTEGER array, dimension ( N ).
*>         On entry, GIVPTR( I ) records the number of Givens
*>         rotations performed on the I-th problem on the computation
*>         tree.
*> \endverbatim
*>
*> \param[in] GIVCOL
*> \verbatim
*>          GIVCOL is INTEGER array, dimension ( LDGCOL, 2 * NLVL ).
*>         On entry, for each I, GIVCOL(*, 2 * I - 1: 2 * I) records the
*>         locations of Givens rotations performed on the I-th level on
*>         the computation tree.
*> \endverbatim
*>
*> \param[in] LDGCOL
*> \verbatim
*>          LDGCOL is INTEGER, LDGCOL = > N.
*>         The leading dimension of arrays GIVCOL and PERM.
*> \endverbatim
*>
*> \param[in] PERM
*> \verbatim
*>          PERM is INTEGER array, dimension ( LDGCOL, NLVL ).
*>         On entry, PERM(*, I) records permutations done on the I-th
*>         level of the computation tree.
*> \endverbatim
*>
*> \param[in] GIVNUM
*> \verbatim
*>          GIVNUM is REAL array, dimension ( LDU, 2 * NLVL ).
*>         On entry, GIVNUM(*, 2 *I -1 : 2 * I) records the C- and S-
*>         values of Givens rotations performed on the I-th level on the
*>         computation tree.
*> \endverbatim
*>
*> \param[in] C
*> \verbatim
*>          C is REAL array, dimension ( N ).
*>         On entry, if the I-th subproblem is not square,
*>         C( I ) contains the C-value of a Givens rotation related to
*>         the right null space of the I-th subproblem.
*> \endverbatim
*>
*> \param[in] S
*> \verbatim
*>          S is REAL array, dimension ( N ).
*>         On entry, if the I-th subproblem is not square,
*>         S( I ) contains the S-value of a Givens rotation related to
*>         the right null space of the I-th subproblem.
*> \endverbatim
*>
*> \param[out] WORK
*> \verbatim
*>          WORK is REAL array, dimension (N)
*> \endverbatim
*>
*> \param[out] IWORK
*> \verbatim
*>          IWORK is INTEGER array, dimension (3*N)
*> \endverbatim
*>
*> \param[out] INFO
*> \verbatim
*>          INFO is INTEGER
*>          = 0:  successful exit.
*>          < 0:  if INFO = -i, the i-th argument had an illegal value.
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \date December 2016
*
*> \ingroup realOTHERcomputational
*
*> \par Contributors:
*  ==================
*>
*>     Ming Gu and Ren-Cang Li, Computer Science Division, University of
*>       California at Berkeley, USA \n
*>     Osni Marques, LBNL/NERSC, USA \n
*
*  =====================================================================
      SUBROUTINE SLALSA( ICOMPQ, SMLSIZ, N, NRHS, B, LDB, BX, LDBX, U,
     $                   LDU, VT, K, DIFL, DIFR, Z, POLES, GIVPTR,
     $                   GIVCOL, LDGCOL, PERM, GIVNUM, C, S, WORK,
     $                   IWORK, INFO )
*
*  -- LAPACK computational routine (version 3.7.0) --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*     December 2016
*
*     .. Scalar Arguments ..
      INTEGER            ICOMPQ, INFO, LDB, LDBX, LDGCOL, LDU, N, NRHS,
     $                   SMLSIZ
*     ..
*     .. Array Arguments ..
      INTEGER            GIVCOL( LDGCOL, * ), GIVPTR( * ), IWORK( * ),
     $                   K( * ), PERM( LDGCOL, * )
      REAL               B( LDB, * ), BX( LDBX, * ), C( * ),
     $                   DIFL( LDU, * ), DIFR( LDU, * ),
     $                   GIVNUM( LDU, * ), POLES( LDU, * ), S( * ),
     $                   U( LDU, * ), VT( LDU, * ), WORK( * ),
     $                   Z( LDU, * )
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      REAL               ZERO, ONE
      PARAMETER          ( ZERO = 0.0E0, ONE = 1.0E0 )
*     ..
*     .. Local Scalars ..
      INTEGER            I, I1, IC, IM1, INODE, J, LF, LL, LVL, LVL2,
     $                   ND, NDB1, NDIML, NDIMR, NL, NLF, NLP1, NLVL,
     $                   NR, NRF, NRP1, SQRE
*     ..
*     .. External Subroutines ..
      EXTERNAL           SCOPY, SGEMM, SLALS0, SLASDT, XERBLA
*     ..
*     .. Executable Statements ..
*
*     Test the input parameters.
*
      INFO = 0
*
      IF( ( ICOMPQ.LT.0 ) .OR. ( ICOMPQ.GT.1 ) ) THEN
         INFO = -1
      ELSE IF( SMLSIZ.LT.3 ) THEN
         INFO = -2
      ELSE IF( N.LT.SMLSIZ ) THEN
         INFO = -3
      ELSE IF( NRHS.LT.1 ) THEN
         INFO = -4
      ELSE IF( LDB.LT.N ) THEN
         INFO = -6
      ELSE IF( LDBX.LT.N ) THEN
         INFO = -8
      ELSE IF( LDU.LT.N ) THEN
         INFO = -10
      ELSE IF( LDGCOL.LT.N ) THEN
         INFO = -19
      END IF
      IF( INFO.NE.0 ) THEN
         CALL XERBLA( 'SLALSA', -INFO )
         RETURN
      END IF
*
*     Book-keeping and  setting up the computation tree.
*
      INODE = 1
      NDIML = INODE + N
      NDIMR = NDIML + N
*
      CALL SLASDT( N, NLVL, ND, IWORK( INODE ), IWORK( NDIML ),
     $             IWORK( NDIMR ), SMLSIZ )
*
*     The following code applies back the left singular vector factors.
*     For applying back the right singular vector factors, go to 50.
*
      IF( ICOMPQ.EQ.1 ) THEN
         GO TO 50
      END IF
*
*     The nodes on the bottom level of the tree were solved
*     by SLASDQ. The corresponding left and right singular vector
*     matrices are in explicit form. First apply back the left
*     singular vector matrices.
*
      NDB1 = ( ND+1 ) / 2
      DO 10 I = NDB1, ND
*
*        IC : center row of each node
*        NL : number of rows of left  subproblem
*        NR : number of rows of right subproblem
*        NLF: starting row of the left   subproblem
*        NRF: starting row of the right  subproblem
*
         I1 = I - 1
         IC = IWORK( INODE+I1 )
         NL = IWORK( NDIML+I1 )
         NR = IWORK( NDIMR+I1 )
         NLF = IC - NL
         NRF = IC + 1
         CALL SGEMM( 'T', 'N', NL, NRHS, NL, ONE, U( NLF, 1 ), LDU,
     $               B( NLF, 1 ), LDB, ZERO, BX( NLF, 1 ), LDBX )
         CALL SGEMM( 'T', 'N', NR, NRHS, NR, ONE, U( NRF, 1 ), LDU,
     $               B( NRF, 1 ), LDB, ZERO, BX( NRF, 1 ), LDBX )
   10 CONTINUE
*
*     Next copy the rows of B that correspond to unchanged rows
*     in the bidiagonal matrix to BX.
*
      DO 20 I = 1, ND
         IC = IWORK( INODE+I-1 )
         CALL SCOPY( NRHS, B( IC, 1 ), LDB, BX( IC, 1 ), LDBX )
   20 CONTINUE
*
*     Finally go through the left singular vector matrices of all
*     the other subproblems bottom-up on the tree.
*
      J = 2**NLVL
      SQRE = 0
*
      DO 40 LVL = NLVL, 1, -1
         LVL2 = 2*LVL - 1
*
*        find the first node LF and last node LL on
*        the current level LVL
*
         IF( LVL.EQ.1 ) THEN
            LF = 1
            LL = 1
         ELSE
            LF = 2**( LVL-1 )
            LL = 2*LF - 1
         END IF
         DO 30 I = LF, LL
            IM1 = I - 1
            IC = IWORK( INODE+IM1 )
            NL = IWORK( NDIML+IM1 )
            NR = IWORK( NDIMR+IM1 )
            NLF = IC - NL
            NRF = IC + 1
            J = J - 1
            CALL SLALS0( ICOMPQ, NL, NR, SQRE, NRHS, BX( NLF, 1 ), LDBX,
     $                   B( NLF, 1 ), LDB, PERM( NLF, LVL ),
     $                   GIVPTR( J ), GIVCOL( NLF, LVL2 ), LDGCOL,
     $                   GIVNUM( NLF, LVL2 ), LDU, POLES( NLF, LVL2 ),
     $                   DIFL( NLF, LVL ), DIFR( NLF, LVL2 ),
     $                   Z( NLF, LVL ), K( J ), C( J ), S( J ), WORK,
     $                   INFO )
   30    CONTINUE
   40 CONTINUE
      GO TO 90
*
*     ICOMPQ = 1: applying back the right singular vector factors.
*
   50 CONTINUE
*
*     First now go through the right singular vector matrices of all
*     the tree nodes top-down.
*
      J = 0
      DO 70 LVL = 1, NLVL
         LVL2 = 2*LVL - 1
*
*        Find the first node LF and last node LL on
*        the current level LVL.
*
         IF( LVL.EQ.1 ) THEN
            LF = 1
            LL = 1
         ELSE
            LF = 2**( LVL-1 )
            LL = 2*LF - 1
         END IF
         DO 60 I = LL, LF, -1
            IM1 = I - 1
            IC = IWORK( INODE+IM1 )
            NL = IWORK( NDIML+IM1 )
            NR = IWORK( NDIMR+IM1 )
            NLF = IC - NL
            NRF = IC + 1
            IF( I.EQ.LL ) THEN
               SQRE = 0
            ELSE
               SQRE = 1
            END IF
            J = J + 1
            CALL SLALS0( ICOMPQ, NL, NR, SQRE, NRHS, B( NLF, 1 ), LDB,
     $                   BX( NLF, 1 ), LDBX, PERM( NLF, LVL ),
     $                   GIVPTR( J ), GIVCOL( NLF, LVL2 ), LDGCOL,
     $                   GIVNUM( NLF, LVL2 ), LDU, POLES( NLF, LVL2 ),
     $                   DIFL( NLF, LVL ), DIFR( NLF, LVL2 ),
     $                   Z( NLF, LVL ), K( J ), C( J ), S( J ), WORK,
     $                   INFO )
   60    CONTINUE
   70 CONTINUE
*
*     The nodes on the bottom level of the tree were solved
*     by SLASDQ. The corresponding right singular vector
*     matrices are in explicit form. Apply them back.
*
      NDB1 = ( ND+1 ) / 2
      DO 80 I = NDB1, ND
         I1 = I - 1
         IC = IWORK( INODE+I1 )
         NL = IWORK( NDIML+I1 )
         NR = IWORK( NDIMR+I1 )
         NLP1 = NL + 1
         IF( I.EQ.ND ) THEN
            NRP1 = NR
         ELSE
            NRP1 = NR + 1
         END IF
         NLF = IC - NL
         NRF = IC + 1
         CALL SGEMM( 'T', 'N', NLP1, NRHS, NLP1, ONE, VT( NLF, 1 ), LDU,
     $               B( NLF, 1 ), LDB, ZERO, BX( NLF, 1 ), LDBX )
         CALL SGEMM( 'T', 'N', NRP1, NRHS, NRP1, ONE, VT( NRF, 1 ), LDU,
     $               B( NRF, 1 ), LDB, ZERO, BX( NRF, 1 ), LDBX )
   80 CONTINUE
*
   90 CONTINUE
*
      RETURN
*
*     End of SLALSA
*
      END