omp reduction

OMP reduction is a directive in OpenMP (Open Multi-Processing) that allows for parallel reduction operations in shared memory parallel programming. It is used to perform operations like summation, product, finding the maximum or minimum value, etc., on a set of values with the help of multiple threads.

The reduction clause specifies that each thread has its private copy of a variable, and at the end of the reduction construct, the private copies are combined into a shared variable using a specific reduction operator. The reduction operator can be any associative and commutative operation, such as addition (+), multiplication (*), bitwise OR (|), bitwise AND (&), etc.

For example, if you have a loop that performs addition on an array of values and you want to parallelize it using OpenMP, you can use the reduction clause to ensure that each thread has its private sum, and at the end, the private sums are combined into a shared sum.

Here's an example of using the reduction clause in OpenMP for parallel summation:

#include <omp.h>

int main() {
    int n = 100;
    int array[n];
    int sum = 0;

    // Initialize array with values

    #pragma omp parallel for reduction(+:sum)
    for (int i = 0; i < n; i++) {
        sum += array[i];
    }

    printf("Sum: %d\n", sum);

    return 0;
}

In this example, the `#pragma omp parallel for reduction(+:sum)` directive parallelizes the loop and performs summation on the `array` using multiple threads. The `reduction(+:sum)` clause specifies that each thread has its private `sum`, and at the end of the loop, the private sums are combined into the shared `sum` using the addition operator (`+`).

I hope this answers your question. Let me know if you have any further queries!