prime_openmp, a C code which counts the number of primes between 1 and N, using OpenMP to carry out the calculation in parallel.
The algorithm is completely naive. For each integer I, it simply checks whether any smaller J evenly divides it. The total amount of work for a given N is thus roughly proportional to 1/2*N^2.
This program is mainly a starting point for investigations into parallelization.
Here are the counts of the number of primes for some selected values of N:
|N||Pi(N), Number of Primes|
In the BASH shell, the program could be run with 2 threads using the commands:
export OMP_NUM_THREADS=2 ./prime_openmp
The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.
prime_openmp is available in a C version and a C++ version and a FORTRAN90 version.
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