SCATTER(3PVM) PVM Version 3.4 SCATTER(3PVM)NAME
pvm_scatter - Sends to each member of a group a section of an array
from a specified member of the group.
SYNOPSIS
C int info = pvm_scatter( void *result, void *data,
int count, int datatype, int msgtag,
char *group, int rootginst)
Fortran call pvmfscatter(result, data, count, datatype,
msgtag, group, rootginst, info)
PARAMETERS
result Pointer to the starting address of an array of length count of
datatype which will be overwritten by the message from the
specified root member of the group.
data On the root this is a pointer to the starting address of an
array datatype of local values which are to be distributed to
the members of the group. If n is the number of members in the
group, then this array of datatype should be of length at least
n*count. This argument is meaningful only on the root.
count Integer specifying the number of elements of datatype to be
sent to each member of the group from the root.
datatype
Integer specifying the type of the entries in the result and
data arrays. (See below for defined types.)
msgtag Integer message tag supplied by the user. msgtag should be >=
0. It allows the user's program to distinguish between differ‐
ent kinds of messages.
group Character string group name of an existing group.
rootginst
Integer instance number of group member who performs the scat‐
ter of its array to the members of the group.
info Integer status code returned by the routine. Values less than
zero indicate an error.
DESCRIPTIONpvm_scatter() performs a scatter of data from the specified root member
of the group to each of the members of the group, including itself.
All group members must call pvm_scatter(), each receives a portion of
the data array from the root in their local result array. It is as if
the root node sends to the ith member of the group count elements from
its array data starting at offset i*count from the beginning of the
data array. And, it is as if, each member of the group performs a cor‐
responding receive of count values of datatype into its result array.
The root task is identified by its instance number in the group.
C and Fortran defined datatypes are:
C datatypes FORTRAN datatypes
-----------------------------------
PVM_BYTE BYTE1
PVM_SHORT INTEGER2
PVM_INT INTEGER4
PVM_FLOAT REAL4
PVM_CPLX COMPLEX8
PVM_DOUBLE REAL8
PVM_DCPLX COMPLEX16
PVM_LONG
In using the scatter and gather routines, keep in mind that C stores
multidimensional arrays in row order, typically starting with an ini‐
tial index of 0; whereas, Fortran stores arrays in column order, typi‐
cally starting with an offset of 1.
The current algorithm is very simple and robust. A future implementa‐
tion may make more efficient use of the architecture to allow greater
parallelism.
EXAMPLES
C:
info = pvm_scatter(&getmyrow, &matrix, 10, PVM_INT,
msgtag, "workers", rootginst);
Fortran:
CALL PVMFSCATTER(GETMYCOLUMN, MATRIX, COUNT, INTEGER4,
& MTAG, 'workers', ROOT, INFO)
ERRORS
These error conditions can be returned by pvm_scatter
PvmNoInst
Calling task is not in the group
PvmBadParam
The datatype specified is not appropriate
PvmSysErr
Pvm system error
SEE ALSOpvm_bcast(3PVM), pvm_barrier(3PVM), pvm_psend(3PVM)
21 April, 1994 SCATTER(3PVM)
