PCSRSCL - multiplie an N-element complex distributed vector sub( X ) by the real
scalar 1/a
- SUBROUTINE PCSRSCL(
- N, SA, SX, IX, JX, DESCX, INCX )
INTEGER IX, INCX, JX, N REAL SA INTEGER DESCX( * ) COMPLEX SX( * )
PCSRSCL multiplies an N-element complex distributed vector sub( X ) by the real
scalar 1/a. This is done without overflow or underflow as long as the final
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.
- N (global input) pointer to INTEGER
- The number of components of the distributed vector sub( X ). N >=
0.
- SA (global input) REAL
- 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) COMPLEX 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.