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SUBROUTINE PZGETF2( M, N, A, IA, JA, DESCA, IPIV, INFO )
*
* -- ScaLAPACK routine (version 1.7) --
* University of Tennessee, Knoxville, Oak Ridge National Laboratory,
* and University of California, Berkeley.
* May 1, 1997
*
* .. Scalar Arguments ..
INTEGER IA, INFO, JA, M, N
* ..
* .. Array Arguments ..
INTEGER DESCA( * ), IPIV( * )
COMPLEX*16 A( * )
* ..
*
* Purpose
* =======
*
* PZGETF2 computes an LU factorization of a general M-by-N
* distributed matrix sub( A ) = A(IA:IA+M-1,JA:JA+N-1) using
* partial pivoting with row interchanges.
*
* The factorization has the form sub( A ) = P * L * U, where P is a
* permutation matrix, L is lower triangular with unit diagonal
* elements (lower trapezoidal if m > n), and U is upper triangular
* (upper trapezoidal if m < n).
*
* This is the right-looking Parallel Level 2 BLAS version of the
* algorithm.
*
* 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
*
* This routine requires N <= NB_A-MOD(JA-1, NB_A) and square block
* decomposition ( MB_A = 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 ).
* NB_A-MOD(JA-1, NB_A) >= N >= 0.
*
* A (local input/local output) COMPLEX*16 pointer into the
* local memory to an array of dimension (LLD_A, LOCc(JA+N-1)).
* On entry, this array contains the local pieces of the M-by-N
* distributed matrix sub( A ). On exit, this array contains
* the local pieces of the factors L and U from the factoriza-
* tion sub( A ) = P*L*U; the unit diagonal elements of L are
* not stored.
*
* 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.
*
* IPIV (local output) INTEGER array, dimension ( LOCr(M_A)+MB_A )
* This array contains the pivoting information.
* IPIV(i) -> The global row local row i was swapped with.
* This array is tied to the distributed matrix A.
*
* INFO (local output) INTEGER
* = 0: successful exit
* < 0: If the i-th argument is an array and the j-entry had
* an illegal value, then INFO = -(i*100+j), if the i-th
* argument is a scalar and had an illegal value, then
* INFO = -i.
* > 0: If INFO = K, U(IA+K-1,JA+K-1) is exactly zero.
* The factorization has been completed, but the factor U
* is exactly singular, and division by zero will occur if
* it is used to solve a system of equations.
*
* =====================================================================
*
* .. 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 )
COMPLEX*16 ONE, ZERO
PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 )
* ..
* .. Local Scalars ..
CHARACTER ROWBTOP
INTEGER I, IACOL, IAROW, ICOFF, ICTXT, IIA, IROFF, J,
$ JJA, MN, MYCOL, MYROW, NPCOL, NPROW
COMPLEX*16 GMAX
* ..
* .. External Subroutines ..
EXTERNAL BLACS_ABORT, BLACS_GRIDINFO, CHK1MAT, IGEBR2D,
$ IGEBS2D, INFOG2L, PB_TOPGET, PXERBLA, PZAMAX,
$ PZGERU, PZSCAL, PZSWAP
* ..
* .. Intrinsic Functions ..
INTRINSIC MIN, MOD
* ..
* .. Executable Statements ..
*
* Get grid parameters.
*
ICTXT = DESCA( CTXT_ )
CALL BLACS_GRIDINFO( ICTXT, NPROW, NPCOL, MYROW, MYCOL )
*
* Test the input parameters.
*
INFO = 0
IF( NPROW.EQ.-1 ) THEN
INFO = -(600+CTXT_)
ELSE
CALL CHK1MAT( M, 1, N, 2, IA, JA, DESCA, 6, INFO )
IF( INFO.EQ.0 ) THEN
IROFF = MOD( IA-1, DESCA( MB_ ) )
ICOFF = MOD( JA-1, DESCA( NB_ ) )
IF( N+ICOFF.GT.DESCA( NB_ ) ) THEN
INFO = -2
ELSE IF( IROFF.NE.0 ) THEN
INFO = -4
ELSE IF( ICOFF.NE.0 ) THEN
INFO = -5
ELSE IF( DESCA( MB_ ).NE.DESCA( NB_ ) ) THEN
INFO = -(600+NB_)
END IF
END IF
END IF
*
IF( INFO.NE.0 ) THEN
CALL PXERBLA( ICTXT, 'PZGETF2', -INFO )
CALL BLACS_ABORT( ICTXT, 1 )
RETURN
END IF
*
* Quick return if possible
*
IF( M.EQ.0 .OR. N.EQ.0 )
$ RETURN
*
MN = MIN( M, N )
CALL INFOG2L( IA, JA, DESCA, NPROW, NPCOL, MYROW, MYCOL, IIA, JJA,
$ IAROW, IACOL )
CALL PB_TOPGET( ICTXT, 'Broadcast', 'Rowwise', ROWBTOP )
*
IF( MYCOL.EQ.IACOL ) THEN
DO 10 J = JA, JA+MN-1
I = IA + J - JA
*
* Find pivot and test for singularity.
*
CALL PZAMAX( M-J+JA, GMAX, IPIV( IIA+J-JA ), A, I, J,
$ DESCA, 1 )
IF( GMAX.NE.ZERO ) THEN
*
* Apply the row interchanges to columns JA:JA+N-1
*
CALL PZSWAP( N, A, I, JA, DESCA, DESCA( M_ ), A,
$ IPIV( IIA+J-JA ), JA, DESCA, DESCA( M_ ) )
*
* Compute elements I+1:IA+M-1 of J-th column.
*
IF( J-JA+1.LT.M )
$ CALL PZSCAL( M-J+JA-1, ONE / GMAX, A, I+1, J,
$ DESCA, 1 )
ELSE IF( INFO.EQ.0 ) THEN
INFO = J - JA + 1
END IF
*
* Update trailing submatrix
*
IF( J-JA+1.LT.MN ) THEN
CALL PZGERU( M-J+JA-1, N-J+JA-1, -ONE, A, I+1, J, DESCA,
$ 1, A, I, J+1, DESCA, DESCA( M_ ), A, I+1,
$ J+1, DESCA )
END IF
10 CONTINUE
*
CALL IGEBS2D( ICTXT, 'Rowwise', ROWBTOP, MN, 1, IPIV( IIA ),
$ MN )
*
ELSE
*
CALL IGEBR2D( ICTXT, 'Rowwise', ROWBTOP, MN, 1, IPIV( IIA ),
$ MN, MYROW, IACOL )
*
END IF
*
RETURN
*
* End of PZGETF2
*
END
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