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DOUBLE PRECISION FUNCTION PDLANGE( NORM, M, N, A, IA, JA, DESCA,
$ WORK )
*
* -- ScaLAPACK auxiliary routine (version 1.7) --
* University of Tennessee, Knoxville, Oak Ridge National Laboratory,
* and University of California, Berkeley.
* May 1, 1997
*
* .. Scalar Arguments ..
CHARACTER NORM
INTEGER IA, JA, M, N
* ..
* .. Array Arguments ..
INTEGER DESCA( * )
DOUBLE PRECISION A( * ), WORK( * )
* ..
*
* Purpose
* =======
*
* PDLANGE returns the value of the one norm, or the Frobenius norm,
* or the infinity norm, or the element of largest absolute value of a
* distributed matrix sub( A ) = A(IA:IA+M-1, JA:JA+N-1).
*
* PDLANGE returns the value
*
* ( max(abs(A(i,j))), NORM = 'M' or 'm' with IA <= i <= IA+M-1,
* ( and JA <= j <= JA+N-1,
* (
* ( norm1( sub( A ) ), NORM = '1', 'O' or 'o'
* (
* ( normI( sub( A ) ), NORM = 'I' or 'i'
* (
* ( normF( sub( A ) ), NORM = 'F', 'f', 'E' or 'e'
*
* where norm1 denotes the one norm of a matrix (maximum column sum),
* normI denotes the infinity norm of a matrix (maximum row sum) and
* normF denotes the Frobenius norm of a matrix (square root of sum of
* squares). Note that max(abs(A(i,j))) is not a matrix norm.
*
* 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
* =========
*
* NORM (global input) CHARACTER
* Specifies the value to be returned in PDLANGE as described
* above.
*
* M (global input) INTEGER
* The number of rows to be operated on i.e the number of rows
* of the distributed submatrix sub( A ). When M = 0, PDLANGE
* is set to zero. 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 ). When N = 0,
* PDLANGE is set to zero. N >= 0.
*
* A (local input) DOUBLE PRECISION pointer into the local memory
* to an array of dimension (LLD_A, LOCc(JA+N-1)) containing the
* local pieces of the distributed matrix sub( A ).
*
* 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.
*
* WORK (local workspace) DOUBLE PRECISION array dimension (LWORK)
* LWORK >= 0 if NORM = 'M' or 'm' (not referenced),
* Nq0 if NORM = '1', 'O' or 'o',
* Mp0 if NORM = 'I' or 'i',
* 0 if NORM = 'F', 'f', 'E' or 'e' (not referenced),
* where
*
* IROFFA = MOD( IA-1, MB_A ), ICOFFA = MOD( JA-1, NB_A ),
* IAROW = INDXG2P( IA, MB_A, MYROW, RSRC_A, NPROW ),
* IACOL = INDXG2P( JA, NB_A, MYCOL, CSRC_A, NPCOL ),
* Mp0 = NUMROC( M+IROFFA, MB_A, MYROW, IAROW, NPROW ),
* Nq0 = NUMROC( N+ICOFFA, NB_A, MYCOL, IACOL, NPCOL ),
*
* INDXG2P and NUMROC 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 )
DOUBLE PRECISION ONE, ZERO
PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 )
* ..
* .. Local Scalars ..
INTEGER I, IACOL, IAROW, ICTXT, II, ICOFF, IOFFA,
$ IROFF, J, JJ, LDA, MP, MYCOL, MYROW, NPCOL,
$ NPROW, NQ
DOUBLE PRECISION SCALE, SUM, VALUE
* ..
* .. Local Arrays ..
DOUBLE PRECISION RWORK( 2 )
* ..
* .. External Subroutines ..
EXTERNAL BLACS_GRIDINFO, DCOMBSSQ, DGEBR2D,
$ DGEBS2D, DGAMX2D, DGSUM2D, DLASSQ,
$ INFOG2L, PDTREECOMB
* ..
* .. External Functions ..
LOGICAL LSAME
INTEGER IDAMAX, NUMROC
EXTERNAL LSAME, IDAMAX, NUMROC
* ..
* .. Intrinsic Functions ..
INTRINSIC ABS, MAX, MIN, MOD, SQRT
* ..
* .. Executable Statements ..
*
* Get grid parameters.
*
ICTXT = DESCA( CTXT_ )
CALL BLACS_GRIDINFO( ICTXT, NPROW, NPCOL, MYROW, MYCOL )
*
CALL INFOG2L( IA, JA, DESCA, NPROW, NPCOL, MYROW, MYCOL, II, JJ,
$ IAROW, IACOL )
IROFF = MOD( IA-1, DESCA( MB_ ) )
ICOFF = MOD( JA-1, DESCA( NB_ ) )
MP = NUMROC( M+IROFF, DESCA( MB_ ), MYROW, IAROW, NPROW )
NQ = NUMROC( N+ICOFF, DESCA( NB_ ), MYCOL, IACOL, NPCOL )
IF( MYROW.EQ.IAROW )
$ MP = MP - IROFF
IF( MYCOL.EQ.IACOL )
$ NQ = NQ - ICOFF
LDA = DESCA( LLD_ )
*
IF( MIN( M, N ).EQ.0 ) THEN
*
VALUE = ZERO
*
ELSE IF( LSAME( NORM, 'M' ) ) THEN
*
* Find max(abs(A(i,j))).
*
VALUE = ZERO
IF( NQ.GT.0 .AND. MP.GT.0 ) THEN
IOFFA = (JJ-1)*LDA
DO 20 J = JJ, JJ+NQ-1
DO 10 I = II, MP+II-1
VALUE = MAX( VALUE, ABS( A( IOFFA+I ) ) )
10 CONTINUE
IOFFA = IOFFA + LDA
20 CONTINUE
END IF
CALL DGAMX2D( ICTXT, 'All', ' ', 1, 1, VALUE, 1, I, J, -1,
$ 0, 0 )
*
ELSE IF( LSAME( NORM, 'O' ) .OR. NORM.EQ.'1' ) THEN
*
* Find norm1( sub( A ) ).
*
IF( NQ.GT.0 ) THEN
IOFFA = ( JJ - 1 ) * LDA
DO 40 J = JJ, JJ+NQ-1
SUM = ZERO
IF( MP.GT.0 ) THEN
DO 30 I = II, MP+II-1
SUM = SUM + ABS( A( IOFFA+I ) )
30 CONTINUE
END IF
IOFFA = IOFFA + LDA
WORK( J-JJ+1 ) = SUM
40 CONTINUE
END IF
*
* Find sum of global matrix columns and store on row 0 of
* process grid
*
CALL DGSUM2D( ICTXT, 'Columnwise', ' ', 1, NQ, WORK, 1,
$ 0, MYCOL )
*
* Find maximum sum of columns for 1-norm
*
IF( MYROW.EQ.0 ) THEN
IF( NQ.GT.0 ) THEN
VALUE = WORK( IDAMAX( NQ, WORK, 1 ) )
ELSE
VALUE = ZERO
END IF
CALL DGAMX2D( ICTXT, 'Rowwise', ' ', 1, 1, VALUE, 1, I, J,
$ -1, 0, 0 )
END IF
*
ELSE IF( LSAME( NORM, 'I' ) ) THEN
*
* Find normI( sub( A ) ).
*
IF( MP.GT.0 ) THEN
IOFFA = II + ( JJ - 1 ) * LDA
DO 60 I = II, II+MP-1
SUM = ZERO
IF( NQ.GT.0 ) THEN
DO 50 J = IOFFA, IOFFA + NQ*LDA - 1, LDA
SUM = SUM + ABS( A( J ) )
50 CONTINUE
END IF
WORK( I-II+1 ) = SUM
IOFFA = IOFFA + 1
60 CONTINUE
END IF
*
* Find sum of global matrix rows and store on column 0 of
* process grid
*
CALL DGSUM2D( ICTXT, 'Rowwise', ' ', MP, 1, WORK, MAX( 1, MP ),
$ MYROW, 0 )
*
* Find maximum sum of rows for supnorm
*
IF( MYCOL.EQ.0 ) THEN
IF( MP.GT.0 ) THEN
VALUE = WORK( IDAMAX( MP, WORK, 1 ) )
ELSE
VALUE = ZERO
END IF
CALL DGAMX2D( ICTXT, 'Columnwise', ' ', 1, 1, VALUE, 1, I,
$ J, -1, 0, 0 )
END IF
*
ELSE IF( ( LSAME( NORM, 'F' ) ) .OR. ( LSAME( NORM, 'E' ) ) ) THEN
*
* Find normF( sub( A ) ).
*
SCALE = ZERO
SUM = ONE
IOFFA = II + ( JJ - 1 ) * LDA
IF( NQ.GT.0 ) THEN
DO 70 J = IOFFA, IOFFA + NQ*LDA - 1, LDA
CALL DLASSQ( MP, A( J ), 1, SCALE, SUM )
70 CONTINUE
END IF
*
* Perform the global scaled sum
*
RWORK( 1 ) = SCALE
RWORK( 2 ) = SUM
CALL PDTREECOMB( ICTXT, 'All', 2, RWORK, 0, 0, DCOMBSSQ )
VALUE = RWORK( 1 ) * SQRT( RWORK( 2 ) )
*
END IF
*
IF( MYROW.EQ.0 .AND. MYCOL.EQ.0 ) THEN
CALL DGEBS2D( ICTXT, 'All', ' ', 1, 1, VALUE, 1 )
ELSE
CALL DGEBR2D( ICTXT, 'All', ' ', 1, 1, VALUE, 1, 0, 0 )
END IF
*
PDLANGE = VALUE
*
RETURN
*
* End of PDLANGE
*
END
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