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SUBROUTINE PSGEQRRV( M, N, A, IA, JA, DESCA, TAU, WORK )
*
* -- ScaLAPACK routine (version 1.7) --
* University of Tennessee, Knoxville, Oak Ridge National Laboratory,
* and University of California, Berkeley.
* May 28, 2001
*
* .. Scalar Arguments ..
INTEGER IA, JA, M, N
* ..
* .. Array Arguments ..
INTEGER DESCA( * )
REAL A( * ), TAU( * ), WORK( * )
* ..
*
* Purpose
* =======
*
* PSGEQRRV computes sub( A ) = A(IA:IA+M-1,JA:JA+N-1) from Q, R
* computed by PSGEQRF.
*
* Notes
* =====
*
* Each global data object is described by an associated description
* vector. This vector stores the information required to establish
* the mapping between an object element and its corresponding process
* and memory location.
*
* Let A be a generic term for any 2D block cyclicly distributed array.
* Such a global array has an associated description vector DESCA.
* In the following comments, the character _ should be read as
* "of the global array".
*
* NOTATION STORED IN EXPLANATION
* --------------- -------------- --------------------------------------
* DTYPE_A(global) DESCA( DTYPE_ )The descriptor type. In this case,
* DTYPE_A = 1.
* CTXT_A (global) DESCA( CTXT_ ) The BLACS context handle, indicating
* the BLACS process grid A is distribu-
* ted over. The context itself is glo-
* bal, but the handle (the integer
* value) may vary.
* M_A (global) DESCA( M_ ) The number of rows in the global
* array A.
* N_A (global) DESCA( N_ ) The number of columns in the global
* array A.
* MB_A (global) DESCA( MB_ ) The blocking factor used to distribute
* the rows of the array.
* NB_A (global) DESCA( NB_ ) The blocking factor used to distribute
* the columns of the array.
* RSRC_A (global) DESCA( RSRC_ ) The process row over which the first
* row of the array A is distributed.
* CSRC_A (global) DESCA( CSRC_ ) The process column over which the
* first column of the array A is
* distributed.
* LLD_A (local) DESCA( LLD_ ) The leading dimension of the local
* array. LLD_A >= MAX(1,LOCr(M_A)).
*
* Let K be the number of rows or columns of a distributed matrix,
* and assume that its process grid has dimension p x q.
* LOCr( K ) denotes the number of elements of K that a process
* would receive if K were distributed over the p processes of its
* process column.
* Similarly, LOCc( K ) denotes the number of elements of K that a
* process would receive if K were distributed over the q processes of
* its process row.
* The values of LOCr() and LOCc() may be determined via a call to the
* ScaLAPACK tool function, NUMROC:
* LOCr( M ) = NUMROC( M, MB_A, MYROW, RSRC_A, NPROW ),
* LOCc( N ) = NUMROC( N, NB_A, MYCOL, CSRC_A, NPCOL ).
* An upper bound for these quantities may be computed by:
* LOCr( M ) <= ceil( ceil(M/MB_A)/NPROW )*MB_A
* LOCc( N ) <= ceil( ceil(N/NB_A)/NPCOL )*NB_A
*
* Arguments
* =========
*
* M (global input) INTEGER
* The number of rows to be operated on, i.e. the number of rows
* of the distributed submatrix sub( A ). M >= 0.
*
* N (global input) INTEGER
* The number of columns to be operated on, i.e. the number of
* columns of the distributed submatrix sub( A ). N >= 0.
*
* A (local input/local output) REAL pointer into the
* local memory to an array of dimension (LLD_A, LOCc(JA+N-1)).
* On entry, sub( A ) contains the the factors Q and R computed
* by PSGEQRF. On exit, the original matrix is restored.
*
* IA (global input) INTEGER
* The row index in the global array A indicating the first
* row of sub( A ).
*
* JA (global input) INTEGER
* The column index in the global array A indicating the
* first column of sub( A ).
*
* DESCA (global and local input) INTEGER array of dimension DLEN_.
* The array descriptor for the distributed matrix A.
*
* TAU (local input) REAL, array, dimension
* LOCc(JA+MIN(M,N)-1). This array contains the scalar factors
* TAU of the elementary reflectors computed by PSGEQRF. TAU
* is tied to the distributed matrix A.
*
* WORK (local workspace) REAL array, dimension (LWORK)
* LWORK = NB_A * ( 2*Mp0 + Nq0 + NB_A ), where
* Mp0 = NUMROC( M+IROFF, MB_A, MYROW, IAROW, NPROW ) * NB_A,
* Nq0 = NUMROC( N+ICOFF, NB_A, MYCOL, IACOL, NPCOL ) * MB_A,
* IROFF = MOD( IA-1, MB_A ), ICOFF = MOD( JA-1, NB_A ),
* IAROW = INDXG2P( IA, DESCA( MB_ ), MYROW, DESCA( RSRC_ ),
* NPROW ),
* IACOL = INDXG2P( JA, DESCA( NB_ ), MYCOL, DESCA( CSRC_ ),
* NPCOL ),
* and NUMROC, INDXG2P are ScaLAPACK tool functions;
* MYROW, MYCOL, NPROW and NPCOL can be determined by calling
* the subroutine BLACS_GRIDINFO.
*
* =====================================================================
*
* .. Parameters ..
INTEGER BLOCK_CYCLIC_2D, CSRC_, CTXT_, DLEN_, DTYPE_,
$ LLD_, MB_, M_, NB_, N_, RSRC_
PARAMETER ( BLOCK_CYCLIC_2D = 1, DLEN_ = 9, DTYPE_ = 1,
$ CTXT_ = 2, M_ = 3, N_ = 4, MB_ = 5, NB_ = 6,
$ RSRC_ = 7, CSRC_ = 8, LLD_ = 9 )
REAL ONE, ZERO
PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 )
* ..
* .. Local Scalars ..
CHARACTER COLBTOP, ROWBTOP
INTEGER IACOL, IAROW, I, ICTXT, IIA, IPT, IPV, IPW,
$ IROFF, IV, J, JB, JJA, JL, JN, K, MP, MYCOL,
$ MYROW, NPCOL, NPROW
* ..
* .. Local Arrays ..
INTEGER DESCV( DLEN_ )
* ..
* .. External Subroutines ..
EXTERNAL BLACS_GRIDINFO, DESCSET, INFOG2L, PSLACPY,
$ PSLARFB, PSLARFT, PSLASET, PB_TOPGET,
$ PB_TOPSET
* ..
* .. External Functions ..
INTEGER ICEIL, INDXG2P, NUMROC
EXTERNAL ICEIL, INDXG2P, NUMROC
* ..
* .. Intrinsic Functions ..
INTRINSIC MAX, MIN, MOD
* ..
* .. Executable Statements ..
*
* Get grid parameters
*
ICTXT = DESCA( CTXT_ )
CALL BLACS_GRIDINFO( ICTXT, NPROW, NPCOL, MYROW, MYCOL )
*
IROFF = MOD( IA-1, DESCA( MB_ ) )
CALL INFOG2L( IA, JA, DESCA, NPROW, NPCOL, MYROW, MYCOL, IIA, JJA,
$ IAROW, IACOL )
MP = NUMROC( M+IROFF, DESCA( MB_ ), MYROW, IAROW, NPROW )
IPV = 1
IPT = IPV + MP * DESCA( NB_ )
IPW = IPT + DESCA( NB_ ) * DESCA( NB_ )
CALL PB_TOPGET( ICTXT, 'Broadcast', 'Rowwise', ROWBTOP )
CALL PB_TOPGET( ICTXT, 'Broadcast', 'Columnwise', COLBTOP )
CALL PB_TOPSET( ICTXT, 'Broadcast', 'Rowwise', 'D-ring' )
CALL PB_TOPSET( ICTXT, 'Broadcast', 'Columnwise', ' ' )
*
K = MIN( M, N )
JN = MIN( ICEIL( JA, DESCA( NB_ ) ) * DESCA( NB_ ), JA+K-1 )
JL = MAX( ( (JA+K-2) / DESCA( NB_ ) ) * DESCA( NB_ ) + 1, JA )
*
CALL DESCSET( DESCV, M+IROFF, DESCA( NB_ ), DESCA( MB_ ),
$ DESCA( NB_ ), IAROW, INDXG2P( JL, DESCA( NB_ ),
$ MYCOL, DESCA( CSRC_ ), NPCOL ), ICTXT,
$ MAX( 1, MP ) )
*
DO 10 J = JL, JN+1, -DESCA( NB_ )
JB = MIN( JA+K-J, DESCA( NB_ ) )
I = IA + J - JA
IV = 1 + J - JA + IROFF
*
* Compute upper triangular matrix T
*
CALL PSLARFT( 'Forward', 'Columnwise', M-I+IA, JB, A, I, J,
$ DESCA, TAU, WORK( IPT ), WORK( IPW ) )
*
* Copy Householder vectors into workspace
*
CALL PSLACPY( 'Lower', M-I+IA, JB, A, I, J, DESCA, WORK( IPV ),
$ IV, 1, DESCV )
CALL PSLASET( 'Upper', M-I+IA, JB, ZERO, ONE, WORK( IPV ), IV,
$ 1, DESCV )
*
* Zeroes the strict lower triangular part of sub( A ) to get
* block column of R
*
CALL PSLASET( 'Lower', M-I+IA-1, JB, ZERO, ZERO, A, I+1, J,
$ DESCA )
*
* Apply block Householder transformation
*
CALL PSLARFB( 'Left', 'No transpose', 'Forward', 'Columnwise',
$ M-I+IA, N-J+JA, JB, WORK( IPV ), IV, 1, DESCV,
$ WORK( IPT ), A, I, J, DESCA, WORK( IPW ) )
*
DESCV( CSRC_ ) = MOD( DESCV( CSRC_ ) + NPCOL - 1, NPCOL )
*
10 CONTINUE
*
* Handle first block separately
*
JB = JN - JA + 1
*
* Compute upper triangular matrix T
*
CALL PSLARFT( 'Forward', 'Columnwise', M, JB, A, IA, JA, DESCA,
$ TAU, WORK( IPT ), WORK( IPW ) )
*
* Copy Householder vectors into workspace
*
CALL PSLACPY( 'Lower', M, JB, A, IA, JA, DESCA, WORK( IPV ),
$ IROFF+1, 1, DESCV )
CALL PSLASET( 'Upper', M, JB, ZERO, ONE, WORK, IROFF+1, 1, DESCV )
*
* Zeroes the strict lower triangular part of sub( A ) to get block
* column of R
*
CALL PSLASET( 'Lower', M-1, JB, ZERO, ZERO, A, IA+1, JA, DESCA )
*
* Apply block Householder transformation
*
CALL PSLARFB( 'Left', 'No transpose', 'Forward', 'Columnwise', M,
$ N, JB, WORK( IPV ), IROFF+1, 1, DESCV, WORK( IPT ),
$ A, IA, JA, DESCA, WORK( IPW ) )
*
CALL PB_TOPSET( ICTXT, 'Broadcast', 'Rowwise', ROWBTOP )
CALL PB_TOPSET( ICTXT, 'Broadcast', 'Columnwise', COLBTOP )
*
RETURN
*
* End of PSGEQRRV
*
END
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