PCLACP3(3)    ScaLAPACK routine of NEC Numeric Library Collection   PCLACP3(3)



NAME
       PCLACP3  -  i  an  auxiliary routine that copies from a global parallel
       array into a local replicated array or vise versa

SYNOPSIS
       SUBROUTINE PCLACP3( M, I, A, DESCA, B, LDB, II, JJ, REV )

           INTEGER         I, II, JJ, LDB, M, REV

           INTEGER         DESCA( * )

           COMPLEX         A( * ), B( LDB, * )

PURPOSE
       PCLACP3 is an auxiliary routine that  copies  from  a  global  parallel
       array  into  a  local replicated array or vise versa. Notice that   the
       entire submatrix that is copied gets placed on one node or
         more.  The receiving node can be specified precisely, or all nodes
         can receive, or just one row or column of nodes.


       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
       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 col-
       umn.
       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
               M is the order of the square submatrix that is copied.  M >= 0.
               Unchanged on exit

       I       (global input) INTEGER
               A(I,I)  is  the  global  location that the copying starts from.
               Unchanged on exit.

       A       (global input/output) COMPLEX array, dimension
               (DESCA(LLD_),*) On entry, the parallel matrix to be copied into
               or  from.   On  exit,  if REV=1, the copied data.  Unchanged on
               exit if REV=0.

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

       B       (local input/output) COMPLEX array of size (LDB,M)
               If  REV=0,  this  is  the   global   portion   of   the   array
               A(I:I+M-1,I:I+M-1).  If REV=1, this is the unchanged on exit.

       LDB     (local input) INTEGER
               The leading dimension of B.

       II      (global input) INTEGER
               By  using  REV  0 & 1, data can be sent out and returned again.
               If REV=0, then II is destination  row  index  for  the  node(s)
               receiving  the replicated B.  If II>=0,JJ>=0, then node (II,JJ)
               receives the data If II=-1,JJ>=0, then all rows  in  column  JJ
               receive  the  data  If  II>=0,JJ=-1,  then  all  cols in row II
               receive the data If II=-1,JJ=-1, then  all  nodes  receive  the
               data If REV<>0, then II is the source row index for the node(s)
               sending the replicated B.

       JJ      (global input) INTEGER
               Similar description as II above

       REV     (global input) INTEGER
               Use REV = 0 to send global A into locally replicated B (on node
               (II,JJ)).   Use REV <> 0 to send locally replicated B from node
               (II,JJ) to its owner (which changes depending on  its  location
               in A) into the global A.

FURTHER DETAILS
       Implemented by:  M. Fahey, May 28, 1999




ScaLAPACK routine               31 October 2017                     PCLACP3(3)