Reduction
C | FORTRAN-legacy | FORTRAN-2008
MPI_LAND
Definition
MPI_LAND is a predefined reduction operation that will calculate the logical and of the values reduced.
Example
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <mpi.h>
/**
* @brief Illustrates how to use a logical and reduction operation.
* @details This application consists of a logical and reduction; every MPI process
* sends its value for reduction before the logical and of these values is stored in
* the root MPI process. It can be visualised as follows, with MPI process 0 as
* root:
*
* +-----------+ +-----------+ +-----------+ +-----------+
* | Process 0 | | Process 1 | | Process 2 | | Process 3 |
* +-+-------+-+ +-+-------+-+ +-+-------+-+ +-+-------+-+
* | Value | | Value | | Value | | Value |
* | true | | true | | true | | false |
* +-------+ +-------+ +-------+ +-------+
* \ | | /
* \ | | /
* \ | | /
* \ | | /
* +-----+-----+-----+-----+
* |
* +---+---+
* | LAND |
* +---+---+
* |
* +---+---+
* | false |
* +-+-------+-+
* | Process 0 |
* +-----------+
**/
int main(int argc, char* argv[])
{
MPI_Init(&argc, &argv);
// Get the number of processes and check only 4 are used.
int size;
MPI_Comm_size(MPI_COMM_WORLD, &size);
if(size != 4)
{
printf("This application is meant to be run with 4 processes.\n");
MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
}
// Determine root's rank
int root_rank = 0;
// Get my rank
int my_rank;
MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
// Each MPI process sends its rank to reduction, root MPI process collects the result
bool my_value = (my_rank != 3);
bool reduction_result = false;
MPI_Reduce(&my_value, &reduction_result, 1, MPI_C_BOOL, MPI_LAND, root_rank, MPI_COMM_WORLD);
if(my_rank == root_rank)
{
printf("The logical and of all values is %s.\n", reduction_result ? "true" : "false");
}
MPI_Finalize();
return EXIT_SUCCESS;
}