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NAME

       PZTRTI2  -  compute  the inverse of a complex upper or lower triangular
       block matrix sub( A ) = A(IA:IA+N-1,JA:JA+N-1)

SYNOPSIS

       SUBROUTINE PZTRTI2( UPLO, DIAG, N, A, IA, JA, DESCA, INFO )

           CHARACTER       DIAG, UPLO

           INTEGER         IA, INFO, JA, N

           INTEGER         DESCA( * )

           COMPLEX*16      A( * )

PURPOSE

       PZTRTI2 computes the inverse of a complex  upper  or  lower  triangular
       block  matrix  sub( A ) = A(IA:IA+N-1,JA:JA+N-1). This matrix should be
       contained in one and only one process memory space (local operation).

       Notes
       =====

       Each global data object  is  described  by  an  associated  description
       vector.   This  vector stores the information required to establish the
       mapping 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
       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

       UPLO    (global input) CHARACTER*1
               = ’U’:  sub( A ) is upper triangular;
               = ’L’:  sub( A ) is lower triangular.

       DIAG    (global input) CHARACTER*1
               = ’N’:  sub( A ) is non-unit triangular
               = ’U’:  sub( A ) is unit triangular

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

       A       (local input/local output) COMPLEX*16 pointer into the
               local memory to an  array  of  dimension  (LLD_A,LOCc(JA+N-1)),
               this  array  contains the local pieces of the triangular matrix
               sub( A ). If UPLO = ’U’, the leading  N-by-N  upper  triangular
               part  of  the  matrix  sub(  A  ) contains the upper triangular
               matrix, and the strictly lower triangular part of sub( A  )  is
               not  referenced.   If  UPLO  =  ’L’,  the  leading N-by-N lower
               triangular part of the matrix  sub(  A  )  contains  the  lower
               triangular  matrix,  and  the strictly upper triangular part of
               sub( A ) is  not  referenced.  If  DIAG  =  ’U’,  the  diagonal
               elements of sub( A ) are also not referenced and are assumed to
               be 1.  On  exit,  the  (triangular)  inverse  of  the  original
               matrix, in the same storage format.

       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.

       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.