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PSGGQRF(l)			       )			    PSGGQRF(l)

NAME
       PSGGQRF	-  compute  a generalized QR factorization of an N-by-M	matrix
       sub( A )	= A(IA:IA+N-1,JA:JA+M-1) and an	 N-by-P	 matrix	 sub(  B  )  =
       B(IB:IB+N-1,JB:JB+P-1)

SYNOPSIS
       SUBROUTINE PSGGQRF( N,  M, P, A,	IA, JA,	DESCA, TAUA, B,	IB, JB,	DESCB,
			   TAUB, WORK, LWORK, INFO )

	   INTEGER	   IA, IB, INFO, JA, JB, LWORK,	M, N, P

	   INTEGER	   DESCA( * ), DESCB( *	)

	   REAL		   A( *	), B( *	), TAUA( * ), TAUB( * ), WORK( * )

PURPOSE
       PSGGQRF computes	a generalized QR factorization	of  an	N-by-M	matrix
       sub(  A	)  =  A(IA:IA+N-1,JA:JA+M-1)  and  an N-by-P matrix sub( B ) =
       B(IB:IB+N-1,JB:JB+P-1):
		   sub(	A ) = Q*R,	  sub( B ) = Q*T*Z,

       where Q is an N-by-N orthogonal matrix, Z is a  P-by-P  orthogonal  ma-
       trix, and R and T assume	one of the forms:

       if N >= M,  R = ( R11 ) M  ,   or if N <	M,  R =	( R11  R12 ) N,
		       (  0  ) N-M			   N   M-N
			  M

       where R11 is upper triangular, and

       if N <= P,  T = ( 0  T12	) N,   or if N > P,  T = ( T11 ) N-P,
			P-N  N				 ( T21 ) P
							    P

       where T12 or T21	is upper triangular.

       In  particular,	if sub(	B ) is square and nonsingular, the GQR factor-
       ization of sub( A ) and sub( B )	implicitly gives the QR	 factorization
       of inv( sub( B )	)* sub(	A ):

		    inv( sub( B	) )*sub( A )= Z'*(inv(T)*R)

       where  inv(  sub( B ) ) denotes the inverse of the matrix sub( B	), and
       Z' denotes the transpose	of matrix Z.

       Notes
       =====

       Each global data	object is described by an associated description  vec-
       tor.  This vector stores	the information	required to establish the map-
       ping 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 as-
       sume that its process grid has dimension	p x q.
       LOCr(  K	) denotes the number of	elements of K that a process would re-
       ceive 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
       N       (global input) INTEGER
	       The number of rows to be	operated on i.e	the number of rows  of
	       the distributed submatrices sub(	A ) and	sub( B ). N >= 0.

       M       (global input) INTEGER
	       The  number of columns to be operated on	i.e the	number of col-
	       umns of the distributed submatrix sub( A	).  M >= 0.

       P       (global input) INTEGER
	       The number of columns to	be operated on i.e the number of  col-
	       umns of the distributed submatrix sub( B	).  P >= 0.

       A       (local input/local output) REAL pointer into the
	       local  memory  to  an array of dimension	(LLD_A,	LOCc(JA+M-1)).
	       On entry, the local pieces of  the  N-by-M  distributed	matrix
	       sub( A )	which is to be factored.  On exit, the elements	on and
	       above the diagonal of sub( A ) contain the min(N,M) by M	 upper
	       trapezoidal matrix R (R is upper	triangular if N	>= M); the el-
	       ements below the	diagonal, with the array TAUA,	represent  the
	       orthogonal matrix Q as a	product	of min(N,M) elementary reflec-
	       tors (see Further Details).  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.

       TAUA    (local output) REAL, array, dimension
	       LOCc(JA+MIN(N,M)-1).  This  array  contains  the	scalar factors
	       TAUA of the elementary reflectors which represent the  orthogo-
	       nal  matrix  Q.	TAUA is	tied to	the distributed	matrix A. (see
	       Further Details).   B	    (local  input/local	 output)  REAL
	       pointer	into the local memory to an array of dimension (LLD_B,
	       LOCc(JB+P-1)).  On entry, the local pieces of the  N-by-P  dis-
	       tributed	matrix sub( B )	which is to be factored. On exit, if N
	       <= P, the upper triangle	of B(IB:IB+N-1,JB+P-N:JB+P-1) contains
	       the N by	N upper	triangular matrix T; if	N > P, the elements on
	       and above the (N-P)-th subdiagonal contain the  N  by  P	 upper
	       trapezoidal  matrix  T;	the remaining elements,	with the array
	       TAUB, represent the orthogonal matrix Z as a product of elemen-
	       tary  reflectors	(see Further Details).	IB	(global	input)
	       INTEGER The row index in	the  global  array  B  indicating  the
	       first row of sub( B ).

       JB      (global input) INTEGER
	       The  column  index  in  the global array	B indicating the first
	       column of sub( B	).

       DESCB   (global and local input)	INTEGER	array of dimension DLEN_.
	       The array descriptor for	the distributed	matrix B.

       TAUB    (local output) REAL, array, dimension LOCr(IB+N-1)
	       This array contains the scalar factors of  the  elementary  re-
	       flectors	which represent	the orthogonal unitary matrix Z.  TAUB
	       is tied to the distributed matrix B (see	Further	Details).

       WORK    (local workspace/local output) REAL array,
	       dimension (LWORK) On exit, WORK(1) returns the minimal and  op-
	       timal LWORK.

       LWORK   (local or global	input) INTEGER
	       The dimension of	the array WORK.	 LWORK is local	input and must
	       be at least LWORK >= MAX( NB_A *	( NpA0 + MqA0 +	NB_A  ),  MAX(
	       (NB_A*(NB_A-1))/2, (PqB0	+ NpB0)*NB_A ) + NB_A *	NB_A, MB_B * (
	       NpB0 + PqB0 + MB_B ) ), 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 ), NpA0	 =  NUMROC(  N+IROFFA,
	       MB_A,  MYROW,  IAROW, NPROW ), MqA0   = NUMROC( M+ICOFFA, NB_A,
	       MYCOL, IACOL, NPCOL ),

	       IROFFB =	MOD( IB-1, MB_B	), ICOFFB = MOD( JB-1, NB_B  ),	 IBROW
	       =  INDXG2P( IB, MB_B, MYROW, RSRC_B, NPROW ), IBCOL  = INDXG2P(
	       JB, NB_B, MYCOL,	CSRC_B,	NPCOL ), NpB0	 =  NUMROC(  N+IROFFB,
	       MB_B,  MYROW,  IBROW, NPROW ), PqB0   = NUMROC( P+ICOFFB, NB_B,
	       MYCOL, IBCOL, NPCOL ),

	       and NUMROC, INDXG2P are ScaLAPACK tool functions; MYROW,	MYCOL,
	       NPROW  and  NPCOL  can  be determined by	calling	the subroutine
	       BLACS_GRIDINFO.

	       If LWORK	= -1, then LWORK is global input and a workspace query
	       is assumed; the routine only calculates the minimum and optimal
	       size for	all work arrays. Each of these values is  returned  in
	       the  first  entry of the	corresponding work array, and no error
	       message is issued by PXERBLA.

       INFO    (global 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.

FURTHER	DETAILS
       The matrix Q is represented as a	product	of elementary reflectors

	  Q = H(ja) H(ja+1) . .	. H(ja+k-1), where k = min(n,m).

       Each H(i) has the form

	  H(i) = I - taua * v *	v'

       where taua is a real scalar, and	v is a real vector with
       v(1:i-1)	= 0 and	v(i) = 1; v(i+1:n) is stored on	exit in
       A(ia+i:ia+n-1,ja+i-1), and taua in TAUA(ja+i-1).
       To form Q explicitly, use ScaLAPACK subroutine PSORGQR.
       To use Q	to update another matrix, use ScaLAPACK	subroutine PSORMQR.

       The matrix Z is represented as a	product	of elementary reflectors

	  Z = H(ib) H(ib+1) . .	. H(ib+k-1), where k = min(n,p).

       Each H(i) has the form

	  H(i) = I - taub * v *	v'

       where taub is a real scalar, and	v is a real vector with
       v(p-k+i+1:p) = 0	and v(p-k+i) = 1; v(1:p-k+i-1) is stored  on  exit  in
       B(ib+n-k+i-1,jb:jb+p-k+i-2),  and  taub in TAUB(ib+n-k+i-1).  To	form Z
       explicitly, use ScaLAPACK subroutine PSORGRQ.
       To use Z	to update another matrix, use ScaLAPACK	subroutine PSORMRQ.

       Alignment requirements
       ======================

       The distributed submatrices sub(	A ) and	sub(  B	 )  must  verify  some
       alignment properties, namely the	following expression should be true:

       ( MB_A.EQ.MB_B .AND. IROFFA.EQ.IROFFB .AND. IAROW.EQ.IBROW )

ScaLAPACK version 1.7		13 August 2001			    PSGGQRF(l)

NAME | SYNOPSIS | PURPOSE | ARGUMENTS | FURTHER DETAILS

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