PCTRTI2  compute the inverse of a complex upper or lower triangular block
matrix sub( A ) = A(IA:IA+N1,JA:JA+N1)
 SUBROUTINE PCTRTI2(
 UPLO, DIAG, N, A, IA, JA, DESCA, INFO )
CHARACTER DIAG, UPLO INTEGER IA, INFO, JA, N INTEGER DESCA( * ) COMPLEX A( * )
PCTRTI2 computes the inverse of a complex upper or lower triangular block matrix
sub( A ) = A(IA:IA+N1,JA:JA+N1). 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
 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 nonunit 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 pointer into the
 local memory to an array of dimension (LLD_A,LOCc(JA+N1)), this array
contains the local pieces of the triangular matrix sub( A ). If UPLO =
'U', the leading NbyN 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 NbyN
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 ith argument is an array and the jentry had an illegal
value, then INFO = (i*100+j), if the ith argument is a scalar and had an
illegal value, then INFO = i.