PZUNG2R(3)    ScaLAPACK routine of NEC Numeric Library Collection   PZUNG2R(3)



NAME
       PZUNG2R  -  generate  an  M-by-N  complex distributed matrix Q denoting
       A(IA:IA+M-1,JA:JA+N-1) with orthonormal columns, which  is  defined  as
       the  first N columns of a product of K elementary reflectors of order M
       Q = H(1) H(2)

SYNOPSIS
       SUBROUTINE PZUNG2R( M, N, K, A, IA, JA, DESCA, TAU, WORK, LWORK, INFO )

           INTEGER         IA, INFO, JA, K, LWORK, M, N

           INTEGER         DESCA( * )

           COMPLEX*16      A( * ), TAU( * ), WORK( * )

PURPOSE
       PZUNG2R  generates  an  M-by-N  complex  distributed  matrix Q denoting
       A(IA:IA+M-1,JA:JA+N-1) with orthonormal columns, which  is  defined  as
       the  first N columns of a product of K elementary reflectors of order M
       Q = H(1) H(2) . . . H(k) as returned by PZGEQRF.


       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
               The number of rows to be operated on i.e the number of rows  of
               the distributed submatrix Q. M >= 0.

       N       (global input) INTEGER
               The  number  of  columns  to  be  operated on i.e the number of
               columns of the distributed submatrix Q. M >= N >= 0.

       K       (global input) INTEGER
               The number of elementary reflectors whose product  defines  the
               matrix Q. N >= K >= 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, the j-th column must contain the  vector  which  defines
               the  elementary  reflector H(j), JA <= j <= JA+K-1, as returned
               by  PZGEQRF  in  the  K   columns   of   its   array   argument
               A(IA:*,JA:JA+K-1).  On  exit,  this  array  contains  the local
               pieces of the M-by-N distributed matrix Q.

       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.

       TAU     (local input) COMPLEX*16, array, dimension LOCc(JA+K-1).
               This array contains the scalar factors TAU(j) of the elementary
               reflectors  H(j)  as  returned  by PZGEQRF.  TAU is tied to the
               distributed matrix A.

       WORK    (local workspace/local output) COMPLEX*16 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 >= MpA0 + MAX( 1, NqA0 ), 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 ),

               INDXG2P and NUMROC 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    (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.



ScaLAPACK routine               31 October 2017                     PZUNG2R(3)