detail.h

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#ifndef GOOSEFEM_DETAIL_H
#define GOOSEFEM_DETAIL_H
 
namespace GooseFEM {
namespace detail {
 
template <size_t nd, typename = void>
struct tensor {
};
 
template <size_t nd>
struct tensor<nd, typename std::enable_if_t<nd == 2>> {
    template <class T>
    static double inv(const T& A, T& Ainv)
    {
        double det = A(0, 0) * A(1, 1) - A(0, 1) * A(1, 0);
 
        Ainv(0, 0) = A(1, 1) / det;
        Ainv(0, 1) = -1.0 * A(0, 1) / det;
        Ainv(1, 0) = -1.0 * A(1, 0) / det;
        Ainv(1, 1) = A(0, 0) / det;
 
        return det;
    }
};
 
template <size_t nd>
struct tensor<nd, typename std::enable_if_t<nd == 3>> {
    template <class T>
    static double inv(const T& A, T& Ainv)
    {
        double det = (A(0, 0) * A(1, 1) * A(2, 2) + A(0, 1) * A(1, 2) * A(2, 0) +
                      A(0, 2) * A(1, 0) * A(2, 1)) -
                     (A(0, 2) * A(1, 1) * A(2, 0) + A(0, 1) * A(1, 0) * A(2, 2) +
                      A(0, 0) * A(1, 2) * A(2, 1));
 
        Ainv(0, 0) = (A(1, 1) * A(2, 2) - A(1, 2) * A(2, 1)) / det;
        Ainv(0, 1) = (A(0, 2) * A(2, 1) - A(0, 1) * A(2, 2)) / det;
        Ainv(0, 2) = (A(0, 1) * A(1, 2) - A(0, 2) * A(1, 1)) / det;
 
        Ainv(1, 0) = (A(1, 2) * A(2, 0) - A(1, 0) * A(2, 2)) / det;
        Ainv(1, 1) = (A(0, 0) * A(2, 2) - A(0, 2) * A(2, 0)) / det;
        Ainv(1, 2) = (A(0, 2) * A(1, 0) - A(0, 0) * A(1, 2)) / det;
 
        Ainv(2, 0) = (A(1, 0) * A(2, 1) - A(1, 1) * A(2, 0)) / det;
        Ainv(2, 1) = (A(0, 1) * A(2, 0) - A(0, 0) * A(2, 1)) / det;
        Ainv(2, 2) = (A(0, 0) * A(1, 1) - A(0, 1) * A(1, 0)) / det;
 
        return det;
    }
};
 
} // namespace detail
} // namespace GooseFEM
 
#endif