Med Java

User Tools

Site Tools

Trace: • install-oracle19c-centos7
c:mpi:wave-algorithm

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revisionPrevious revision
Next revision		Previous revision
c:mpi:wave-algorithm [2024/01/19 11:42] – removed - external edit (Unknown date) 127.0.0.1c:mpi:wave-algorithm [2025/01/02 18:22] (current) – external edit 127.0.0.1
Line 1: Line 1:
 +====== MPI Wave Algorithm ======
 +
 +Implementing a wave algorithm in MPI involves creating a pattern where each process communicates with its neighbors in a specific sequence. 
 +
 +This can be used to model wave-like propagation of information across the processes. 
 +
 +In this example, let's consider a simple scenario where each process sends a message to its next neighbor, waits to receive a message from its previous neighbor, and then sends a confirmation back.
 +
 +This pattern creates a "wave" of communication that passes through the processes from start to end and then back. It's a basic representation of wave algorithms commonly used in parallel computing for synchronization and data propagation.
 +
 +<code c mpi-wave-algorithm.c>
 +#include <mpi.h>
 +#include <stdio.h>
 +#include <stdlib.h>
 +
 +int main(int argc, char** argv) {
 +    MPI_Init(&argc, &argv);
 +
 +    int world_rank, world_size;
 +    MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
 +    MPI_Comm_size(MPI_COMM_WORLD, &world_size);
 +
 +    int token;
 +
 +    // Create a wave of communication from the first to the last process
 +    if (world_rank != 0) {
 +        MPI_Recv(&token, 1, MPI_INT, world_rank - 1, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
 +        printf("Process %d received token %d from process %d\n", world_rank, token, world_rank - 1);
 +    } else {
 +        // Start the wave
 +        token = -1;
 +    }
 +
 +    MPI_Barrier(MPI_COMM_WORLD);
 +
 +    if (world_rank != world_size - 1) {
 +        token++;
 +        MPI_Send(&token, 1, MPI_INT, world_rank + 1, 0, MPI_COMM_WORLD);
 +        printf("Process %d sent token %d to process %d\n", world_rank, token, world_rank + 1);
 +    }
 +
 +    // Create a wave of confirmation back from the last to the first process
 +    if (world_rank != world_size - 1) {
 +        MPI_Recv(&token, 1, MPI_INT, world_rank + 1, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
 +        printf("Process %d received confirmation %d from process %d\n", world_rank, token, world_rank + 1);
 +    }
 +
 +    MPI_Barrier(MPI_COMM_WORLD);
 +
 +    if (world_rank != 0) {
 +        MPI_Send(&token, 1, MPI_INT, world_rank - 1, 0, MPI_COMM_WORLD);
 +        printf("Process %d sent confirmation %d to process %d\n", world_rank, token, world_rank - 1);
 +    }
 +
 +    MPI_Finalize();
 +    return 0;
 +}
 +</code>
 +
 +The program starts with the first process initializing the wave by sending a token to the next process.
 +
 +Each process waits to receive the token from its previous neighbor, prints a message, and then sends the token to its next neighbor.
 +
 +After reaching the last process, a confirmation wave is sent back in the reverse order.
 +
 +Each process in the reverse wave receives a confirmation token from its next neighbor and sends it to its previous neighbor.
 +
 +**MPI_Barrier** is used to synchronize processes between the forward and reverse waves.
 +
 +This implementation demonstrates a basic wave algorithm where communication flows from the first to the last process and then back. The output will show the flow of tokens and confirmations through the processes.