Here is what the function prototype of MPI_Scatter looks like. Although the root process (process zero) contains the entire array of data, MPI_Scatter will copy the appropriate element into the receiving buffer of the process. The first element (in red) goes to process zero, the second element (in green) goes to process one, and so on. MPI_Scatter takes an array of elements and distributes the elements in the order of process rank. In the illustration, MPI_Bcast takes a single data element at the root process (the red box) and copies it to all other processes. Check out the illustration below for further clarification. MPI_Bcast sends the same piece of data to all processes while MPI_Scatter sends chunks of an array to different processes. The primary difference between MPI_Bcast and MPI_Scatter is small but important. MPI_Scatter involves a designated root process sending data to all processes in a communicator. MPI_Scatter is a collective routine that is very similar to MPI_Bcast (If you are unfamiliar with these terms, please read the previous lesson). This tutorial’s code is under tutorials/mpi-scatter-gather-and-allgather/code. Note - All of the code for this site is on GitHub. We will also cover a variant of MPI_Gather, known as MPI_Allgather.
In this lesson, we are going to expand on collective communication routines by going over two very important routines - MPI_Scatter and MPI_Gather. We covered the most basic collective communication routine - MPI_Bcast. In the previous lesson, we went over the essentials of collective communication. MPI Scatter, Gather, and Allgather Author: Wes Kendall
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