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Template/expval (#489)
* M pennylane_lightning/core/src/bindings/Bindings.hpp; hack `JacobianData` to work with devices. M pennylane_lightning/core/src/simulators/lightning_kokkos/StateVectorKokkos.hpp; `applyMatrix` bugfix: use intermediate hostview to copy matrix data; same bugfix for `getDataVector`. M pennylane_lightning/core/src/simulators/lightning_kokkos/algorithms/AdjointJacobianKokkos.hpp; use copy constructor. M pennylane_lightning/core/src/simulators/lightning_kokkos/measurements/MeasurementsKokkos.hpp; use copy constructor. M pennylane_lightning/core/src/simulators/lightning_kokkos/observables/ObservablesKokkos.hpp; use copy constructor. M requirements-dev.txt; add clang-format-14. * Auto update version * Update changelog. * Auto update version * Auto update version * Add an argument to adjointJacobian to avoid syncing and copying state vector data in adjoint-diff. * Reformat * trigger CI * [skip ci] Update changelog. * Introduce std::unordered_map<std::string, ExpValFunc> expval_funcs_. * Introduce applyExpectationValueFunctor. * Add binding to LKokkos expval(matrix, wires). Combine expval functor calls into two templated methods. Call specialized expval methods when possible. Remove obsolete 'Apply directly' tests. * Update changelog. * Add test for arbitrary expval(Hermitian). * Add getExpectationValueMultiQubitOpFunctor. * Add typename hint for macos. * Add typename macos. * Use Kokkos::ThreadVectorRange policy for innerloop in getExpectationValueMultiQubitOpFunctor. * Auto update version * Auto update version * Couple fix for HIP. * WIP * Add specialized 3-5 qubit expval functors. * Add implementation notes. * [skip ci] Polish getExpValMatrix and limit getExpValNQubitOpFunctor to N == 4 (seems optimal on OPENMP/HIP backends although CUDA can go further). * Fix whitespace warning. * Auto update version * Use simplified bitshifts in 1- & 2-qubit expval kernels. * Update tests. * Update changelog. * Bump pennylane version. * Auto update version * Reimplement expval functors with macros. * Auto update version * Update CHANGELOG.md * Auto update version * trigger CI * trigger CI * Bump Kokkos to 4.1.00 in CI. * Revert kokkos ver. * Add tests for macroed expval functors. * Remove redundant black lines. * Use matrix interface to get expval of HermitianObs in LKokkos. * Cover kokkos_args error. --------- Co-authored-by: Dev version update bot <github-actions[bot]@users.noreply.github.com> Co-authored-by: Amintor Dusko <[email protected]>
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‎.github/CHANGELOG.md

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### Improvements
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* Refactor LKokkos `Measurements` class to use Kokkos `RangePolicy` together with special functors to obtain the expectation value of 1- to 4-wire generic unitary gates. For more than 4 wires, the general implementation using Kokkos `TeamPolicy` is employed to yield the best all-around performance.
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[(#489)] (https://github.com/PennyLaneAI/pennylane-lightning/pull/489)
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* Add tests to increase LKokkos coverage.
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[(#485)](https://github.com/PennyLaneAI/pennylane-lightning/pull/485)
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‎pennylane_lightning/core/_version.py

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Version number (major.minor.patch[-label])
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"""
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__version__ = "0.33.0-dev3"
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__version__ = "0.33.0-dev4"

‎pennylane_lightning/core/src/simulators/lightning_kokkos/gates/README.md

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# Implementation
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## Expval kernels
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The general multi-qubit operator kernel requires a private variable `coeffs_in` to store state vector coefficients.
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In the Kokkos framework, this variable cannot be a private member of the functor, say, because all threads will overwrite it.
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One must then use `TeamPolicy`s together with `scratch_memory_space` which allows creating and manipulating thread-local variables.
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This implementation however appears suboptimal compared with the straightforward `RangePolicy` with bit-injection one.
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The last being more verbose, it is only implemented for 1- and 2-qubit observables.
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It is however possible to generate the code automatically for higher qubit counts with the following Python script.
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```python
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for n_wires in range(1, 6):
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name = f"getExpVal{n_wires}QubitOpFunctor"
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nU = 2**n_wires
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print(
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f"""template <class PrecisionT, std::size_t n_wires> struct {name} {{
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using ComplexT = Kokkos::complex<PrecisionT>;
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using KokkosComplexVector = Kokkos::View<ComplexT *>;
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using KokkosIntVector = Kokkos::View<std::size_t *>;
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KokkosComplexVector arr;
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KokkosComplexVector matrix;
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KokkosIntVector wires;
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std::size_t dim;
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std::size_t num_qubits;
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{name}(const KokkosComplexVector &arr_,
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const std::size_t num_qubits_,
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const KokkosComplexVector &matrix_,
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const KokkosIntVector &wires_) {{
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wires = wires_;
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arr = arr_;
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matrix = matrix_;
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num_qubits = num_qubits_;
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dim = 1U << wires.size();
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}}
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KOKKOS_INLINE_FUNCTION
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void operator()(const std::size_t k, PrecisionT &expval) const {{
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const std::size_t kdim = k * dim;
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"""
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)
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for k in range(nU):
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print(
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f"""
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std::size_t i{k:0{n_wires}b} = kdim | {k};
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for (std::size_t pos = 0; pos < n_wires; pos++) {{
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std::size_t x =
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((i{k:0{n_wires}b} >> (n_wires - pos - 1)) ^
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(i{k:0{n_wires}b} >> (num_qubits - wires(pos) - 1))) &
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1U;
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i{k:0{n_wires}b} = i{k:0{n_wires}b} ^ ((x << (n_wires - pos - 1)) |
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(x << (num_qubits - wires(pos) - 1)));
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}}
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"""
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)
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# print("expval += real(")
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for k in range(nU):
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tmp = f"expval += real(conj(arr(i{k:0{n_wires}b})) * ("
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tmp += f"matrix(0B{k:0{n_wires}b}{0:0{n_wires}b}) * arr(i{0:0{n_wires}b})"
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for j in range(1, nU):
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tmp += (
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f" + matrix(0B{k:0{n_wires}b}{j:0{n_wires}b}) * arr(i{j:0{n_wires}b})"
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)
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print(tmp, end="")
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print("));")
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print("}")
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print("};")
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```

‎pennylane_lightning/core/src/simulators/lightning_kokkos/measurements/CMakeLists.txt

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lightning_observables
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lightning_utils
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${PL_BACKEND}
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${PL_BACKEND}_observables
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${PL_BACKEND}_utils
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)
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