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PCGETRS(l)			       )			    PCGETRS(l)

NAME
       PCGETRS	- solve	a system of distributed	linear equations  op( sub( A )
       ) * X = sub( B )	 with a	general	N-by-N distributed matrix sub( A ) us-
       ing the LU factorization	computed by PCGETRF

SYNOPSIS
       SUBROUTINE PCGETRS( TRANS,  N, NRHS, A, IA, JA, DESCA, IPIV, B, IB, JB,
			   DESCB, INFO )

	   CHARACTER	   TRANS

	   INTEGER	   IA, IB, INFO, JA, JB, N, NRHS

	   INTEGER	   DESCA( * ), DESCB( *	), IPIV( * )

	   COMPLEX	   A( *	), B( *	)

PURPOSE
       PCGETRS solves a	system of distributed linear equations op( sub(	A )  )
       *  X = sub( B ) with a general N-by-N distributed matrix	sub( A ) using
       the  LU	factorization  computed	 by  PCGETRF.	sub(   A   )   denotes
       A(IA:IA+N-1,JA:JA+N-1),	op( A )	= A, A**T or A**H and sub( B ) denotes
       B(IB:IB+N-1,JB:JB+NRHS-1).

       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

       This routine requires square block data decomposition ( MB_A=NB_A ).

ARGUMENTS
       TRANS   (global input) CHARACTER
	       Specifies the form of the system	of equations:
	       = 'N':  sub( A )	   * X = sub( B	)  (No transpose)
	       = 'T':  sub( A )**T * X = sub( B	)  (Transpose)
	       = 'C':  sub( A )**H * X = sub( B	)  (Conjugate transpose)

       N       (global input) INTEGER
	       The number of rows and columns to be operated on, i.e. the  or-
	       der of the distributed submatrix	sub( A ). N >= 0.

       NRHS    (global input) INTEGER
	       The  number of right hand sides,	i.e., the number of columns of
	       the distributed submatrix sub( B	). NRHS	>= 0.

       A       (local input) COMPLEX pointer into the local
	       memory to an array of dimension (LLD_A, LOCc(JA+N-1)).  On  en-
	       try,  this array	contains the local pieces of the factors L and
	       U from the factorization	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 input) 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.

       B       (local input/local output) COMPLEX pointer into the
	       local  memory to	an array of dimension (LLD_B,LOCc(JB+NRHS-1)).
	       On entry, the right hand	sides sub( B ).	On exit, sub( B	 )  is
	       overwritten by the solution distributed matrix X.

       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.

       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.

ScaLAPACK version 1.7		13 August 2001			    PCGETRS(l)

NAME | SYNOPSIS | PURPOSE | ARGUMENTS

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