Pantarhei C Job Examples

C Job Examples

This page contains C job examples for Pantarhei, including a serial C job and a parallel MPI-enabled C job.

Serial C Job

Here is a simple example of a serial C job that performs the same numerical computation as the Python example.

C program (serial_compute.c):

// serial_compute.c
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>

int main() {
    int N_values[] = {20000000, 40000000, 80000000, 160000000};
    int num_tests = sizeof(N_values) / sizeof(N_values[0]);
    
    for (int test = 0; test < num_tests; test++) {
        int N = N_values[test];
        double result = 0.0;
        clock_t start, end;
        
        start = clock();
        
        for (int i = 0; i < N; i++) {
            double x = (double)i * 100.0 / N;
            result += sin(x) * exp(-x / 50.0);
        }
        
        end = clock();
        double elapsed_time = (double)(end - start) / CLOCKS_PER_SEC;
        
        printf("Computed result for %d values: %.6f\n", N, result);
        printf("Elapsed time: %.4f seconds\n", elapsed_time);
    }
    
    return 0;
}

Job submission script (c_serial_job.sh):

#!/bin/bash
# c_serial_job.sh
#SBATCH -J serial_c_job
#SBATCH -p normal
#SBATCH --nodes=1
#SBATCH --ntasks=1
#SBATCH --cpus-per-task=1
#SBATCH -t 00:30:00

# Compile the C program
gcc serial_compute.c -o serial_compute -lm

# Run the compiled program
./serial_compute

Submit the job:

sbatch c_serial_job.sh

Parallel C MPI Job

Here is an example of a parallel MPI job in C that performs the same numerical computation as the Python examples (computing the sum of sin(x) * exp(-x/50.0) for 20 million points).

C MPI program (mpi_compute.c):

// mpi_compute.c
#include <mpi.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main(int argc, char** argv) {
    int rank, size;
    int N_values[] = {20000000, 40000000, 80000000, 160000000};
    int num_tests = sizeof(N_values) / sizeof(N_values[0]);
    
    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    
    for (int test = 0; test < num_tests; test++) {
        int N = N_values[test];
        double local_sum = 0.0, total_sum = 0.0;
        double start_time, end_time;
        
        // Divide work among ranks
        int chunk_size = N / size;
        int start_idx = rank * chunk_size;
        int end_idx = (rank == size - 1) ? N : (rank + 1) * chunk_size;
        
        // Synchronize before timing
        MPI_Barrier(MPI_COMM_WORLD);
        start_time = MPI_Wtime();
        
        // Compute local sum
        for (int i = start_idx; i < end_idx; i++) {
            double x = (double)i * 100.0 / N;
            local_sum += sin(x) * exp(-x / 50.0);
        }
        
        // Reduce all local sums to total sum on rank 0
        MPI_Reduce(&local_sum, &total_sum, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
        
        end_time = MPI_Wtime();
        
        if (rank == 0) {
            printf("Computed result for %d values: %.6f\n", N, total_sum);
            printf("Elapsed time: %.4f seconds\n", end_time - start_time);
        }
    }
    
    MPI_Finalize();
    return 0;
}

Job submission script (mpi_c_job.sh):

#!/bin/bash
# mpi_c_job.sh
#SBATCH -J mpi_c_job
#SBATCH -p normal
#SBATCH --nodes=1
#SBATCH --ntasks=4
#SBATCH --cpus-per-task=1
#SBATCH -t 00:30:00

# Load necessary modules
module purge
module load MVAPICH

# Compile the C MPI program
mpicc mpi_compute.c -o mpi_compute -lm

# Run the MPI application
mpiexec -n 4 ./mpi_compute

Submit the job:

sbatch mpi_c_job.sh

Key points:

• --ntasks=4 launches 4 MPI ranks on 1 node.
• mpicc compiles the C program with MPI support.
• mpiexec -n 4 starts the MPI-enabled C program across all ranks.
• Use MPI for distributed parallelism across cores or nodes.
• The C program performs the same computation as the Python examples for comparison.

Additional Resources

For complete example scripts and job files, visit the Pantarhei examples repository:

https://github.com/kamalcou/pantarhei-examples