Provided by: scalapack-doc_1.5-11_all 
NAME
PDRSCL - multiplie an N-element real distributed vector sub( X ) by the real scalar 1/a
SYNOPSIS
SUBROUTINE PDRSCL( N, SA, SX, IX, JX, DESCX, INCX )
INTEGER IX, INCX, JX, N
DOUBLE PRECISION SA
INTEGER DESCX( * )
DOUBLE PRECISION SX( * )
PURPOSE
PDRSCL multiplies an N-element real distributed vector sub( X ) by the real scalar 1/a. This is done
without overflow or underflow as long as the final result sub( X )/a does not overflow or underflow.
where sub( X ) denotes X(IX:IX+N-1,JX:JX), if INCX = 1,
X(IX:IX,JX:JX+N-1), if INCX = M_X.
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
--------------- -------------- -------------------------------------- DT_A (global) descA[ DT_ ] The
descriptor type. In this case,
DT_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 distribu-
te the rows of the array.
NB_A (global) descA[ NB_ ] The blocking factor used to distribu-
te 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
Because vectors may be seen as particular matrices, a distributed vector is considered to be a
distributed matrix.
ARGUMENTS
N (global input) pointer to INTEGER
The number of components of the distributed vector sub( X ). N >= 0.
SA (global input) DOUBLE PRECISION
The scalar a which is used to divide each component of sub( X ). SA must be >= 0, or the
subroutine will divide by zero.
SX (local input/local output) DOUBLE PRECISION array
containing the local pieces of a distributed matrix of dimension of at least ( (JX-1)*M_X + IX +
( N - 1 )*abs( INCX ) ) This array contains the entries of the distributed vector sub( X ).
IX (global input) pointer to INTEGER
The global row index of the submatrix of the distributed matrix X to operate on.
JX (global input) pointer to INTEGER
The global column index of the submatrix of the distributed matrix X to operate on.
DESCX (global and local input) INTEGER array of dimension 8.
The array descriptor of the distributed matrix X.
INCX (global input) pointer to INTEGER
The global increment for the elements of X. Only two values of INCX are supported in this
version, namely 1 and M_X.