BSSNTildeChristoffel.hpp

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#pragma once
 
#include "../../Core/Tensor.hpp"
#include "../../Core/Vector.hpp"
#include <cassert>
#include <cstddef>
#include <stdexcept>
 
namespace tensorium_RG {
template <typename T> class TildeGamma {
  public:
    static void compute(const tensorium::Tensor<T, 2> &gamma_tilde_inv,
                        const tensorium::Tensor<T, 3> &christoffel,
                        tensorium::Vector<T>          &tildeGamma) {
        if (gamma_tilde_inv.shape() != std::array<size_t, 2>{3, 3})
            throw std::invalid_argument("gamma_tilde_inv must be 3x3");
        if (christoffel.shape() != std::array<size_t, 3>{3, 3, 3})
            throw std::invalid_argument("christoffel must be 3x3x3");
 
        tildeGamma.resize(3);
        for (size_t i = 0; i < 3; ++i) {
            T sum = 0.0;
            for (size_t j = 0; j < 3; ++j) {
                for (size_t k = 0; k < 3; ++k) {
                    sum += gamma_tilde_inv(j, k) * christoffel(i, j, k);
                }
            }
            tildeGamma[i] = sum;
        }
    }
};
} // namespace tensorium_RG