Ubuntu Manpage: pvm_gather - A specified member of the group receives messages from each member of the group and gathers

Provided by: pvm-dev_3.4.5-12.6ubuntu1_amd64

NAME

       pvm_gather  - A specified member of the group receives messages from each member of the group and gathers
       these messages into a single array.

SYNOPSIS

       C    int info = pvm_gather( void *result,  void *data,
                         int count, int datatype, int msgtag,
                         char *group, int rootginst)

       Fortran    call pvmfgather(result, data, count, datatype,
                                  msgtag, group, rootginst, info)

PARAMETERS

       result  On the root this is a pointer to the starting address of an array datatype of local values  which
               are to be accumulated from the members of the group.  If n if 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.

       data    For each group member this is a pointer to the starting address of an array of  length  count  of
               datatype which will be sent to the specified root member of the group.

       count   Integer  specifying  the number of elements of datatype to be sent by each member of the group to
               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 different kinds of messages.

       group   Character string group name of an existing group.

       rootginst
               Integer  instance number of group member who performs the gather of the messages from the members
               of the group.

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

DESCRIPTION

pvm_gather() performs a send of messages from each member of the group to the specified root member of
the group. All group members must call pvm_gather(), each sends its array data of length count of
datatype to the root which accumulates these messages into its result array. It is as if the root
receives count elements of datatype from the ith member of the group and places these values in its
result array starting with offset i*count from the beginning of the 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.

Note: pvm_gather() does not block. If a task calls pvm_gather and then leaves the group before the root
has called pvm_gather an error may occur.

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_gather(&getmatrix, &myrow, 10, PVM_INT,
                             msgtag, "workers", rootginst);

       Fortran:
          CALL PVMFGATHER(GETMATRIX, MYCOLUMN, COUNT, INTEGER4,
         &                MTAG, 'workers', ROOT, INFO)

ERRORS