The latter call will retrieving information from global objects. The displacement, in displ , gives the starting index in the target object where the data in the local vector is to be placed. The scaling parameter, in alpha , allows a multiple of the local data to be added. The data type of the data at the address alpha is assumed to be the same as the data type of the local vector and the target object. Notice that the call is only performed on the node that owns the local vector.
All nodes can simultaneously perform such calls to enter local vectors in global objects.
Now y equals the local vector and x the global, so that the operation performed becomes Again, only the node that owns the local vector makes the call and all nodes can make similar calls simultaneously. It is important to realize that the above calls only initiate the operation. Often, a locally computed vector contributes to a given object, but not as a contiguous sub-vector.