Created
November 13, 2019 09:35
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Greedy MPI_Dims_create
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| /** | |
| * This greedy implementation is exactly what OpenMPI does. | |
| */ | |
| #include <array> | |
| #include <vector> | |
| #include <algorithm> | |
| std::vector<int> prime_factors(int n) { | |
| std::vector<int> fs; | |
| for (int p = 2; n > 1; ++p) { | |
| while (n % p == 0) { | |
| fs.push_back(p); | |
| n /= p; | |
| } | |
| } | |
| return fs; | |
| } | |
| std::array<int, 3> dims_create(int n) { | |
| auto fs = prime_factors(n); | |
| std::array<int, 3> dims = {{1, 1, 1}}; | |
| // Greedy algorithm | |
| // Need to assign largest values first in order for the greedy algorithm | |
| // to work. No need to sort, the result of prime_factors() is sorted. | |
| std::for_each(std::rbegin(fs), std::rend(fs), [&dims](auto f) { | |
| *std::min_element(std::begin(dims), std::end(dims)) *= f; | |
| }); | |
| std::sort(std::rbegin(dims), std::rend(dims)); | |
| return dims; | |
| } |
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