# Examples of OpenMP* Usage

The following examples show how to use the OpenMP* feature.

## A Simple Difference Operator

This example shows a simple parallel loop where the amount of work in each iteration is different. Dynamic scheduling is used to get good load balancing. The for has a nowait because there is an implicit barrier at the end of the parallel region.

 void for_1 (float a[], float b[], int n) {   int i, j;   #pragma omp parallel shared(a,b,n) private(i,j)   {       #pragma omp for schedule(dynamic,1) nowait           for(i = 1; i < n; i++)           {              for(j = 0; j <= i; j++)              b[j + n*i] = (a[j + n*i] + a[j + n*(i-1)])/2.0;           }    } }

## Two Difference Operators

The following example uses two parallel loops fused to reduce fork/join overhead. The first for has a nowait because all the data used in the second loop is different than all the data used in the first loop.

 void for_2 (float a[], float b[], float c[], \ float d[], int n, int m) {   int i, j;   #pragma omp parallel shared(a,b,c,d,n,m) private(i,j)   {     #pragma omp for schedule(dynamic,1) nowait     for(i = 1; i < n; i++)     {       for(j = 0; j <= i; j++)       b[j + n*i] = ( a[j + n*i] + a[j + n*(i-1)] )/2.0;     }       #pragma omp for schedule(dynamic,1) nowait     for(i = 1; i < m; i++)     {       for(j = 0; j <= i; j++)       d[j + m*i] = ( c[j + m*i] + c[j + m*(i-1)] )/2.0;     }   } }