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PSGGRQF(l)			       )			    PSGGRQF(l)

NAME
       PSGGRQF	-  compute  a generalized RQ factorization of an M-by-N	matrix
       sub( A )	= A(IA:IA+M-1,JA:JA+N-1)

SYNOPSIS
       SUBROUTINE PSGGRQF( M, P, N, 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
       PSGGRQF	computes  a  generalized  RQ factorization of an M-by-N	matrix
       sub( A )	= A(IA:IA+M-1,JA:JA+N-1) and  a	 P-by-N	 matrix	 sub(  B  )  =
       B(IB:IB+P-1,JB:JB+N-1):

		   sub(	A ) = R*Q,	  sub( B ) = Z*T*Q,

       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 M <= N,  R = ( 0  R12	) M,   or if M > N,  R = ( R11 ) M-N,
			N-M  M				 ( R21 ) N
							    N

       where R12 or R21	is upper triangular, and

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

       where T11 is upper triangular.

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

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

       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
       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.

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

       N       (global input) INTEGER
	       The  number of columns to be operated on	i.e the	number of col-
	       umns of the distributed submatrices sub(	A ) and	sub( B	).   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, the local pieces of  the  M-by-N  distributed	matrix
	       sub( A )	which is to be factored. On exit, if M <= N, the upper
	       triangle	of A( IA:IA+M-1, JA+N-M:JA+N-1 ) contains the M	 by  M
	       upper triangular	matrix R; if M >= N, the elements on and above
	       the (M-N)-th subdiagonal	contain	the M by N  upper  trapezoidal
	       matrix  R;  the remaining elements, with	the array TAUA,	repre-
	       sent the	orthogonal matrix Q as a product of 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 LOCr(IA+M-1)
	       This array contains the scalar factors of  the  elementary  re-
	       flectors	which represent	the orthogonal unitary 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+N-1)).
	       On  entry,  the	local  pieces of the P-by-N distributed	matrix
	       sub( B )	which is to be factored.  On exit, the elements	on and
	       above  the diagonal of sub( B ) contain the min(P,N) by N upper
	       trapezoidal matrix T (T is upper	triangular if P	>= N); the el-
	       ements  below  the diagonal, with the array TAUB, represent the
	       orthogonal matrix Z as a	product	of elementary 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
	       LOCc(JB+MIN(P,N)-1).  This  array  contains  the	scalar factors
	       TAUB of the elementary reflectors which represent the  orthogo-
	       nal  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 optimal LWORK.

       LWORK   (local or global	input) INTEGER
	       The dimension of	the array WORK.	 LWORK is local	input and must
	       be  at  least LWORK >= MAX( MB_A	* ( MpA0 + NqA0	+ MB_A ), MAX(
	       (MB_A*(MB_A-1))/2, (PpB0	+ NqB0)*MB_A ) + MB_A *	MB_A, NB_B * (
	       PpB0 + NqB0 + NB_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 ), MpA0   = NUMROC( M+IROFFA,
	       MB_A, MYROW, IAROW, NPROW ), NqA0   = NUMROC(  N+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 ), PpB0   = NUMROC( P+IROFFB,
	       MB_B, MYROW, IBROW, NPROW ), NqB0   = NUMROC(  N+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(ia) H(ia+1) . .	. H(ia+k-1), where k = min(m,n).

       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(n-k+i+1:n)  =	0  and v(n-k+i)	= 1; v(1:n-k+i-1) is stored on exit in
       A(ia+m-k+i-1,ja:ja+n-k+i-2), and	taua in	TAUA(ia+m-k+i-1).  To  form  Q
       explicitly, use ScaLAPACK subroutine PSORGRQ.
       To use Q	to update another matrix, use ScaLAPACK	subroutine PSORMRQ.

       The matrix Z is represented as a	product	of elementary reflectors

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

       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(1:i-1)	= 0 and	v(i) = 1; v(i+1:p) is stored on	exit in
       B(ib+i:ib+p-1,jb+i-1), and taub in TAUB(jb+i-1).
       To form Z explicitly, use ScaLAPACK subroutine PSORGQR.
       To use Z	to update another matrix, use ScaLAPACK	subroutine PSORMQR.

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

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

       ( NB_A.EQ.NB_B .AND. ICOFFA.EQ.ICOFFB .AND. IACOL.EQ.IBCOL )

ScaLAPACK version 1.7		13 August 2001			    PSGGRQF(l)

NAME | SYNOPSIS | PURPOSE | ARGUMENTS | FURTHER DETAILS

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