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sum_i_inv
n_thread
repeat
mega_sum
1 + 1/2 + 1/3 + ... + 1/
n_sum
where
n_sum = 1,000,000 *
mega_sum
automatic
,
dynamic thread adjustment is used.
Otherwise, n_thread must be a positive number
specifying the number of OpenMP threads to use.
automatic
,
the number of times to repeat the calculation of the number of zeros
in total interval is automatically determined.
In this case, the rate of execution of the total solution is reported.
If the argument repeat is not equal to automatic,
it must be a positive integer.
In this case repeat determination of the number of times
the calculation of the summation above.
The rate of execution is not reported (it is assumed that the
program execution time is being calculated some other way).
# include <cppad/cppad.hpp>
# ifdef _OPENMP
# include <omp.h>
# endif
# include <cassert>
# ifdef _OPENMP
# include <omp.h>
# endif
# include <cstring>
namespace { // empty namespace
int n_thread;
}
double sum_using_one_thread(int start, int stop)
{ // compute 1./start + 1./(start+1) + ... + 1./(stop-1)
double sum = 0.;
int i = stop;
while( i > start )
{ i--;
sum += 1. / double(i);
}
return sum;
}
double sum_using_multiple_threads(int n_sum)
{ // compute 1. + 1./2 + ... + 1./n_sum
assert( n_sum >= n_thread ); // assume n_sum / n_thread > 1
// limit holds start and stop values for each thread
int limit[n_thread + 1];
int i;
for(i = 1; i < n_thread; i++)
limit[i] = (n_sum * i ) / n_thread;
limit[0] = 1;
limit[n_thread] = n_sum + 1;
// compute sum_one[i] = 1/limit[i] + ... + 1/(limit[i+1} - 1)
double sum_one[n_thread];
//--------------------------------------------------------------------------
# ifdef _OPENMP
# pragma omp parallel for
# endif
for(i = 0; i < n_thread; i++)
sum_one[i] = sum_using_one_thread(limit[i], limit[i+1]);
// -------------------------------------------------------------------------
// compute sum_all = sum_one[0] + ... + sum_one[n_thread-1]
double sum_all = 0.;
for(i = 0; i < n_thread; i++)
sum_all += sum_one[i];
return sum_all;
}
void test_once(double &sum, size_t mega_sum)
{ assert( mega_sum >= 1 );
int n_sum = int(mega_sum * 1000000);
sum = sum_using_multiple_threads(n_sum);
return;
}
void test_repeat(size_t size, size_t repeat)
{ size_t i;
double sum;
for(i = 0; i < repeat; i++)
test_once(sum, size);
return;
}
int main(int argc, char *argv[])
{
using std::cout;
using std::endl;
using CppAD::vector;
char *usage = "sum_i_inv n_thread repeat mega_sum";
if( argc != 4 )
{ std::cerr << usage << endl;
exit(1);
}
argv++;
// n_thread command line argument
if( std::strcmp(*argv, "automatic") == 0 )
n_thread = 0;
else n_thread = std::atoi(*argv);
argv++;
// repeat command line argument
size_t repeat;
if( std::strcmp(*argv, "automatic") == 0 )
repeat = 0;
else
{ assert( std::atoi(*argv) > 0 );
repeat = std::atoi(*argv);
}
argv++;
// mega_sum command line argument
size_t mega_sum;
assert( std::atoi(*argv) > 0 );
mega_sum = size_t( std::atoi(*argv++) );
// minimum time for test (repeat until this much time)
double time_min = 1.;
# ifdef _OPENMP
if( n_thread > 0 )
{ omp_set_dynamic(0); // off dynamic thread adjust
omp_set_num_threads(n_thread); // set the number of threads
}
// now determine the maximum number of threads
n_thread = omp_get_max_threads();
assert( n_thread > 0 );
// No tapes are currently active,
// so we can inform CppAD of the maximum number of threads
CppAD::AD<double>::omp_max_thread(size_t(n_thread));
// inform the user of the maximum number of threads
cout << "OpenMP: version = " << _OPENMP;
cout << ", max number of threads = " << n_thread << endl;
# else
cout << "_OPENMP is not defined, ";
cout << "running in single tread mode" << endl;
n_thread = 1;
# endif
// initialize flag
bool ok = true;
// Correctness check
double sum;
test_once(sum, mega_sum);
double epsilon = 1e-6;
size_t i = 0;
size_t n_sum = mega_sum * 1000000;
while(i < n_sum)
sum -= 1. / double(++i);
ok &= std::fabs(sum) <= epsilon;
if( repeat > 0 )
{ // run the calculation the requested number of time
test_repeat(mega_sum, repeat);
}
else
{ // actually time the calculation
// size of the one test case
vector<size_t> size_vec(1);
size_vec[0] = mega_sum;
// run the test case
vector<size_t> rate_vec =
CppAD::speed_test(test_repeat, size_vec, time_min);
// report results
cout << "mega_sum = " << size_vec[0] << endl;
cout << "repeats per sec = " << rate_vec[0] << endl;
}
// check all the threads for a CppAD memory leak
if( CPPAD_TRACK_COUNT() != 0 )
{ ok = false;
cout << "Error: memory leak detected" << endl;
}
if( ok )
cout << "Correctness Test Passed" << endl;
else cout << "Correctness Test Failed" << endl;
return static_cast<int>( ! ok );
}