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

Provided by: pvm-dev_3.4.6-1build2_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