PDTRTI2(l) ) PDTRTI2(l)NAME
PDTRTI2 - compute the inverse of a real upper or lower triangular block
matrix sub( A ) = A(IA:IA+N-1,JA:JA+N-1)
SYNOPSIS
SUBROUTINE PDTRTI2( UPLO, DIAG, N, A, IA, JA, DESCA, INFO )
CHARACTER DIAG, UPLO
INTEGER IA, INFO, JA, N
INTEGER DESCA( * )
DOUBLE PRECISION A( * )
PURPOSE
PDTRTI2 computes the inverse of a real upper or lower triangular block
matrix sub( A ) = A(IA:IA+N-1,JA:JA+N-1). This matrix should be con‐
tained in one and only one process memory space (local operation).
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
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) DOUBLE PRECISION 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 trian‐
gular 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.
ScaLAPACK version 1.7 13 August 2001 PDTRTI2(l)
