Provided by: scalapack-doc_1.5-11_all bug

NAME

       PCPOSV  -  compute  the  solution to a complex system of linear equations   sub( A ) * X =
       sub( B ),

SYNOPSIS

       SUBROUTINE PCPOSV( UPLO, N, NRHS, A, IA, JA, DESCA, B, IB, JB, DESCB, INFO )

           CHARACTER      UPLO

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

           INTEGER        DESCA( * ), DESCB( * )

           COMPLEX        A( * ), B( * )

PURPOSE

       PCPOSV computes the solution to a complex system of linear equations

       where sub( A ) denotes A(IA:IA+N-1,JA:JA+N-1)  and  is  an  N-by-N  hermitian  distributed
       positive  definite  matrix and X and sub( B ) denoting B(IB:IB+N-1,JB:JB+NRHS-1) are N-by-
       NRHS distributed matrices.

       The Cholesky decomposition is used to factor sub( A ) as

                          sub( A ) = U**H * U,  if UPLO = 'U', or

                          sub( A ) = L * L**H,  if UPLO = 'L',

       where U is an upper triangular matrix and L is a lower triangular  matrix.   The  factored
       form of sub( A ) is then used to solve the system of equations.

       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

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

ARGUMENTS

       UPLO    (global input) CHARACTER
               = 'U':  Upper triangle of sub( A ) is stored;
               = 'L':  Lower triangle of sub( A ) is stored.

       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.

       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/local output) COMPLEX pointer into the
               local memory to an array of dimension (LLD_A, LOCc(JA+N-1)).  On entry, this array
               contains  the  local pieces of the N-by-N symmetric distributed matrix sub( A ) to
               be factored.  If UPLO = 'U', the leading N-by-N upper triangular part of sub( A  )
               contains  the  upper  triangular  part  of  the  matrix,  and  its  strictly lower
               triangular part is not referenced.  If  UPLO  =  'L',  the  leading  N-by-N  lower
               triangular  part  of  sub( A ) contains the lower triangular part of the distribu-
               ted matrix, and its strictly upper triangular part is not referenced. On exit,  if
               INFO  =  0,  this  array  contains  the local pieces of the factor U or L from the
               Cholesky factori- zation sub( A ) = U**H*U or L*L**H.

       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.

       B       (local input/local output) COMPLEX pointer into the
               local memory to an array of dimension (LLD_B,LOC(JB+NRHS-1)).  On entry, the local
               pieces  of  the right hand sides distribu- ted matrix sub( B ). On exit, if INFO =
               0, sub( B ) is over- written with 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.  > 0:  If INFO = K, the leading minor of order K,
               A(IA:IA+K-1,JA:JA+K-1) is not positive definite, and the factorization  could  not
               be completed, and the solution has not been computed.