SCATTER(3PVM) — Subroutines

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

resultPointer 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.

dataOn 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.

countInteger specifying the number of elements of datatype to be sent to each member of the group from the root.

datatypeInteger specifying the type of the entries in the result and data arrays. (See below for defined types.)

msgtagInteger message tag supplied by the user. msgtag should be >= 0. It allows the user’s program to distinguish between different kinds of messages.

groupCharacter string group name of an existing group.

rootginstInteger instance number of group member who performs the scatter of its array to the members of the group.

infoInteger status code returned by the routine. Values less than zero indicate an error.

DESCRIPTION

pvm_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 corresponding 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 initial index of 0; whereas, Fortran stores arrays in column order, typically starting with an offset of 1.

The current algorithm is very simple and robust. A future implementation 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

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