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Merge pull request #10 from qognitive/feature/pauli_string_test
Feature/pauli string test
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,138 @@ | ||
| #ifndef __PAULI_HELPERS_HPP | ||
| #define __PAULI_HELPERS_HPP | ||
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| #include <fmt/format.h> | ||
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| #include <ranges> | ||
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| #include "__pauli_string.hpp" | ||
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| namespace fast_pauli { | ||
| // | ||
| // Helper | ||
| // | ||
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| /** | ||
| * @brief Get the nontrivial sets of pauli matrices given a weight. | ||
| * | ||
| * @param weight | ||
| * @return std::vector<std::string> | ||
| */ | ||
| std::vector<std::string> get_nontrivial_paulis(size_t const weight) { | ||
| // We want to return no paulis for weight 0 | ||
| if (weight == 0) { | ||
| return {}; | ||
| } | ||
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| // For Weight >= 1 | ||
| std::vector<std::string> set_of_nontrivial_paulis{"X", "Y", "Z"}; | ||
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| for (size_t i = 1; i < weight; i++) { | ||
| std::vector<std::string> updated_set_of_nontrivial_paulis; | ||
| for (auto const &str : set_of_nontrivial_paulis) { | ||
| for (auto pauli : {"X", "Y", "Z"}) { | ||
| updated_set_of_nontrivial_paulis.push_back(str + pauli); | ||
| } | ||
| } | ||
| set_of_nontrivial_paulis = std::move(updated_set_of_nontrivial_paulis); | ||
| } | ||
| return set_of_nontrivial_paulis; | ||
| } | ||
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| /** | ||
| * @brief Get all the combinations of k indices for a given array of size n. | ||
| * | ||
| * @param n | ||
| * @param k | ||
| * @return std::vector<std::vector<size_t>> | ||
| */ | ||
| std::vector<std::vector<size_t>> idx_combinations(size_t const n, | ||
| size_t const k) { | ||
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| // TODO this is a very inefficient way to do this | ||
| std::vector<std::vector<size_t>> result; | ||
| std::vector<size_t> bitmask(k, 1); // K leading 1's | ||
| bitmask.resize(n, 0); // N-K trailing 0's | ||
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| do { | ||
| std::vector<size_t> combo; | ||
| for (size_t i = 0; i < n; ++i) { | ||
| if (bitmask[i]) { | ||
| combo.push_back(i); | ||
| } | ||
| } | ||
| result.push_back(combo); | ||
| } while (std::ranges::prev_permutation(bitmask).found); | ||
| return result; | ||
| } | ||
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| /** | ||
| * @brief Calculate all possible PauliStrings for a given number of qubits and | ||
| * weight and return them in lexicographical order. | ||
| * | ||
| * @param n_qubits | ||
| * @param weight | ||
| * @return std::vector<PauliString> | ||
| */ | ||
| std::vector<PauliString> calcutate_pauli_strings(size_t const n_qubits, | ||
| size_t const weight) { | ||
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| // base case | ||
| if (weight == 0) { | ||
| return {PauliString(std::string(n_qubits, 'I'))}; | ||
| } | ||
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| // for weight >= 1 | ||
| std::string base_str(n_qubits, 'I'); | ||
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| auto nontrivial_paulis = get_nontrivial_paulis(weight); | ||
| auto idx_combos = idx_combinations(n_qubits, weight); | ||
| size_t n_pauli_strings = nontrivial_paulis.size() * idx_combos.size(); | ||
| std::vector<PauliString> result(n_pauli_strings); | ||
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| fmt::println( | ||
| "n_qubits = {} weight = {} n_nontrivial_paulis = {} n_combos = {}", | ||
| n_qubits, weight, nontrivial_paulis.size(), idx_combos.size()); | ||
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| // Iterate through all the nontrivial paulis and all the combinations | ||
| for (size_t i = 0; i < nontrivial_paulis.size(); ++i) { | ||
| for (size_t j = 0; j < idx_combos.size(); ++j) { | ||
| // Creating new pauli string at index i*idx_combos.size() + j | ||
| // Overwriting the base string with the appropriate nontrivial paulis | ||
| // at the specified indices | ||
| std::string str = base_str; | ||
| for (size_t k = 0; k < idx_combos[j].size(); ++k) { | ||
| size_t idx = idx_combos[j][k]; | ||
| str[idx] = nontrivial_paulis[i][k]; | ||
| } | ||
| result[i * idx_combos.size() + j] = PauliString(str); | ||
| } | ||
| } | ||
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| return result; | ||
| } | ||
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| /** | ||
| * @brief Calculate all possible PauliStrings for a given number of qubits and | ||
| * all weights less than or equal to a given weight. | ||
| * | ||
| * @param n_qubits | ||
| * @param weight | ||
| * @return std::vector<PauliString> | ||
| */ | ||
| std::vector<PauliString> calculate_pauli_strings_max_weight(size_t n_qubits, | ||
| size_t weight) { | ||
| std::vector<PauliString> result; | ||
| for (size_t i = 0; i <= weight; ++i) { | ||
| auto ps = calcutate_pauli_strings(n_qubits, i); | ||
| result.insert(result.end(), ps.begin(), ps.end()); | ||
| } | ||
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| fmt::println("n_qubits = {} weight = {} n_pauli_strings = {}", n_qubits, | ||
| weight, result.size()); | ||
| return result; | ||
| } | ||
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| } // namespace fast_pauli | ||
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| #endif // __PAULI_HELPERS_HPP |
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