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#pragma once
#include <array>
#include <functional>
#include <eigen3/unsupported/Eigen/CXX11/Tensor>
#include "factorial.hpp"
template <class Scalar>
using Vector = Eigen::Matrix<Scalar, Eigen::Dynamic, 1>;
template <class Scalar>
using Matrix = Eigen::Matrix<Scalar, Eigen::Dynamic, Eigen::Dynamic>;
template <class Scalar, int p>
using Tensor = Eigen::Tensor<Scalar, p>;
template <class Scalar, int p, std::size_t... Indices>
Tensor<Scalar, p> initializeJHelper(unsigned N, std::index_sequence<Indices...>) {
std::array<unsigned, p> Ns;
std::fill_n(Ns.begin(), p, N);
return Tensor<Scalar, p>(std::get<Indices>(Ns)...);
}
template <class Scalar, int p>
Tensor<Scalar, p> initializeJ(unsigned N) {
return initializeJHelper<Scalar, p>(N, std::make_index_sequence<p>());
}
template <class Scalar, int p, std::size_t... Indices>
void setJHelper(Tensor<Scalar, p>& J, const std::array<unsigned, p>& ind, Scalar val, std::index_sequence<Indices...>) {
J(std::get<Indices>(ind)...) = val;
}
template <class Scalar, int p>
void setJ(Tensor<Scalar, p>& J, std::array<unsigned, p> ind, Scalar val) {
do {
setJHelper<Scalar, p>(J, ind, val, std::make_index_sequence<p>());
} while (std::next_permutation(ind.begin(), ind.end()));
}
template <class Scalar, int p, std::size_t... Indices>
Scalar getJHelper(const Tensor<Scalar, p>& J, const std::array<unsigned, p>& ind, std::index_sequence<Indices...>) {
return J(std::get<Indices>(ind)...);
}
template <class Scalar, int p>
Scalar getJ(const Tensor<Scalar, p>& J, const std::array<unsigned, p>& ind) {
return getJHelper<Scalar, p>(J, ind, std::make_index_sequence<p>());
}
template <class Scalar, int p>
void iterateOverHelper(Tensor<Scalar, p>& J,
std::function<void(Tensor<Scalar, p>&, std::array<unsigned, p>)>& f,
unsigned l, std::array<unsigned, p> is) {
if (l == 0) {
f(J, is);
} else {
unsigned iMin;
if (l == p) {
iMin = 0;
} else {
iMin = is[p - l - 1];
}
for (unsigned i = iMin; i < J.dimension(p - 1); i++) {
std::array<unsigned, p> js = is;
js[p - l] = i;
iterateOverHelper<Scalar, p>(J, f, l - 1, js);
}
}
}
template <class Scalar, int p>
void iterateOver(Tensor<Scalar, p>& J, std::function<void(Tensor<Scalar, p>&, std::array<unsigned, p>)>& f) {
std::array<unsigned, p> is;
iterateOverHelper<Scalar, p>(J, f, p, is);
}
template <class Scalar, int p, class Distribution, class Generator>
Tensor<Scalar, p> generateCouplings(unsigned N, Distribution d, Generator& r) {
Tensor<Scalar, p> J = initializeJ<Scalar, p>(N);
std::function<void(Tensor<Scalar, p>&, std::array<unsigned, p>)> setRandom =
[&d, &r] (Tensor<Scalar, p>& JJ, std::array<unsigned, p> ind) {
setJ<Scalar, p>(JJ, ind, d(r));
};
iterateOver<Scalar, p>(J, setRandom);
return J;
}
template <class Real, int p, class Generator>
Tensor<Real, p> generateRealPSpinCouplings(unsigned N, Generator& r) {
Real σp = sqrt(factorial(p) / ((Real)2 * pow(N, p - 1)));
return generateCouplings<Real, p>(N, std::normal_distribution<Real>(0, σp), r);
}
template <class Scalar>
Tensor<Scalar, 3> contractDown(const Tensor<Scalar, 3>& J, const Vector<Scalar>& z) {
return J;
}
const std::array<Eigen::IndexPair<int>, 1> ip00 = {Eigen::IndexPair<int>(0, 0)};
template <class Scalar, int r>
Tensor<Scalar, 3> contractDown(const Tensor<Scalar, r>& J, const Vector<Scalar>& z) {
Tensor<Scalar, 1> zT = Eigen::TensorMap<Tensor<const Scalar, 1>>(z.data(), {z.size()});
Tensor<Scalar, r - 1> Jz = J.contract(zT, ip00);
return contractDown(Jz, z);
}
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