PCHEGST(l) ) PCHEGST(l)NAME
PCHEGST - reduce a complex Hermitian-definite generalized eigenproblem
to standard form
SYNOPSIS
SUBROUTINE PCHEGST( IBTYPE, UPLO, N, A, IA, JA, DESCA, B, IB, JB,
DESCB, SCALE, INFO )
CHARACTER UPLO
INTEGER IA, IB, IBTYPE, INFO, JA, JB, N
REAL SCALE
INTEGER DESCA( * ), DESCB( * )
COMPLEX A( * ), B( * )
PURPOSE
PCHEGST reduces a complex Hermitian-definite generalized eigenproblem
to standard form. In the following sub( A ) denotes A( IA:IA+N-1,
JA:JA+N-1 ) and sub( B ) denotes B( IB:IB+N-1, JB:JB+N-1 ).
If IBTYPE = 1, the problem is sub( A )*x = lambda*sub( B )*x, and sub(
A ) is overwritten by inv(U**H)*sub( A )*inv(U) or inv(L)*sub( A
)*inv(L**H)
If IBTYPE = 2 or 3, the problem is sub( A )*sub( B )*x = lambda*x or
sub( B )*sub( A )*x = lambda*x, and sub( A ) is overwritten by U*sub( A
)*U**H or L**H*sub( A )*L.
sub( B ) must have been previously factorized as U**H*U or L*L**H by
PCPOTRF.
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
IBTYPE (global input) INTEGER
= 1: compute inv(U**H)*sub( A )*inv(U) or inv(L)*sub( A
)*inv(L**H); = 2 or 3: compute U*sub( A )*U**H or L**H*sub( A
)*L.
UPLO (global input) CHARACTER
= 'U': Upper triangle of sub( A ) is stored and sub( B ) is
factored as U**H*U; = 'L': Lower triangle of sub( A ) is
stored and sub( B ) is factored as L*L**H.
N (global input) INTEGER
The order of the matrices sub( A ) and sub( B ). N >= 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
Hermitian distributed matrix sub( A ). If UPLO = 'U', the lead‐
ing N-by-N upper triangular part of sub( A ) contains the upper
triangular part of the matrix, and its strictly lower triangu‐
lar 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 matrix, and its strictly upper triangular part is
not referenced.
On exit, if INFO = 0, the transformed matrix, stored in the
same format as sub( A ).
IA (global input) INTEGER
A's global row index, which points to the beginning of the sub‐
matrix which is to be operated on.
JA (global input) INTEGER
A's global column index, which points to the beginning of the
submatrix which is to be operated on.
DESCA (global and local input) INTEGER array of dimension DLEN_.
The array descriptor for the distributed matrix A.
B (local input) COMPLEX pointer into the local memory
to an array of dimension (LLD_B, LOCc(JB+N-1)). On entry, this
array contains the local pieces of the triangular factor from
the Cholesky factorization of sub( B ), as returned by PCPOTRF.
IB (global input) INTEGER
B's global row index, which points to the beginning of the sub‐
matrix which is to be operated on.
JB (global input) INTEGER
B's global column index, which points to the beginning of the
submatrix which is to be operated on.
DESCB (global and local input) INTEGER array of dimension DLEN_.
The array descriptor for the distributed matrix B.
SCALE (global output) REAL
Amount by which the eigenvalues should be scaled to compensate
for the scaling performed in this routine. At present, SCALE
is always returned as 1.0, it is returned here to allow for
future enhancement.
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.
ScaLAPACK version 1.7 13 August 2001 PCHEGST(l)
