A Simple OpenMP Example and Test
Keywords: simple openmp example test A.1.1c thread purpose source code

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A Simple OpenMP Example and Test
Purpose
This example just demonstrates OpenMP and does not use CppAD at all.
Source Code `

    # include <omp.h>
    # include <limits>
    # include <cmath>
    # include <cassert>
    # define NUMBER_THREADS 4

    namespace {
    	// Beginning of Example A.1.1.1c of OpenMP 2.5 standard document ---------
    	void a1(int n, float *a, float *b)
    	{	int i;
    	# pragma omp parallel for
    		for(i = 1; i < n; i++) /* i is private by default */
    		{	assert( omp_get_num_threads() == NUMBER_THREADS );
    			b[i] = (a[i] + a[i-1]) / float(2);
    		}
    	}
    	// End of Example A.1.1.1c of OpenMP 2.5 standard document ---------------
    }
    bool a11c(void)
    {	bool ok = true;

    	// Test setup
    	int i, n = 1000;
    	float *a = new float[n];
    	float *b = new float[n];
    	for(i = 0; i < n; i++)
    		a[i] = float(i);

    	int n_thread = NUMBER_THREADS;   // number of threads in parallel regions
    	omp_set_dynamic(0);              // off dynamic thread adjust
    	omp_set_num_threads(n_thread);   // set the number of threads

    	a1(n, a, b);

    	// check the result
    	float eps = float(100) * std::numeric_limits<float>::epsilon();
    	for(i = 1; i < n ; i++)
    		ok &= std::fabs( (float(2) * b[i] - a[i] - a[i-1]) / b[i] ) <= eps;

    	delete [] a;
    	delete [] b;

    	return ok;
    }

`

Input File: multi_thread/openmp/a11c_openmp.cpp