pzlase2(3)

NAME

PZLASE2 - initialize an M-by-N distributed matrix sub(

A ) denoting
A(IA:IA+M-1,JA:JA+N-1) to BETA on the diagonal and ALPHA

on the offdiagonals

SYNOPSIS

SUBROUTINE PZLASE2( UPLO, M, N, ALPHA, BETA,  A,  IA,  JA,
DESCA )
    CHARACTER       UPLO
    INTEGER         IA, JA, M, N
    COMPLEX*16      ALPHA, BETA
    INTEGER         DESCA( * )
    COMPLEX*16      A( * )

PURPOSE

PZLASE2 initializes an M-by-N distributed matrix sub(

A ) denoting
A(IA:IA+M-1,JA:JA+N-1) to BETA on the diagonal and ALPHA

on the offdiagonals. PZLASE2 requires that only dimension of the ma

trix operand is
distributed.

Notes
=====

Each global data object is described by an associated de

scription vector. This vector stores the information required to es

tablish the mapping between an object element and its corresponding pro

cess and memory
location.

Let A be a generic term for any 2D block cyclicly dis

tributed 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

distributed over. The context it

self is global, 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

Specifies the part of the distributed matrix

sub( A ) to be
set:
= 'U': Upper triangular part is set; the

strictly lower
triangular part of sub( A ) is not changed; =

'L': Lower
triangular part is set; the strictly upper trian

gular part of
sub( A ) is not changed; Otherwise: All of the

matrix sub( A )
is set.

M (global input) INTEGER

The number of rows to be operated on i.e the num

ber of rows of
the distributed submatrix sub( A ). M >= 0.

N (global input) INTEGER

The number of columns to be operated on i.e

the number of
columns of the distributed submatrix sub( A ). N

>= 0.

ALPHA (global input) COMPLEX*16

The constant to which the offdiagonal elements are

to be set.

BETA (global input) COMPLEX*16

The constant to which the diagonal elements are to

be set.

A (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 distributed matrix

sub( A ) to be
set. On exit, the leading M-by-N submatrix sub( A

) is set as
follows:

if UPLO = 'U', A(IA+i-1,JA+j-1) = ALPHA,

1<=i<=j-1, 1<=j<=N, if
UPLO = 'L', A(IA+i-1,JA+j-1) = ALPHA, j+1<=i<=M,

1<=j<=N, otherwise, A(IA+i-1,JA+j-1) = ALPHA,

1<=i<=M, 1<=j<=N,
IA+i.NE.JA+j, and, for all UPLO,

A(IA+i-1,JA+i-1) = BETA,
1<=i<=min(M,N).

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 indicat

ing the first
column of sub( A ).

DESCA (global and local input) INTEGER array of dimen

sion DLEN_.

The array descriptor for the distributed matrix A.

LAPACK version 1.5 12 May 1997

PZLASE2(l)