Method unflatten_tensor

tests/src/IO/WriterTest.h:113–135

        }

        MatrixF unflatten_tensor(const VectorF& flattened_tensor) {
            const size_t size = flattened_tensor.size();
            const VectorF& A = flattened_tensor;
            MatrixF tensor(3, 3);
            if (size == 3) {
                tensor << A[0], A[2], 0.0,
                          A[2], A[1], 0.0,
                           0.0,  0.0, 0.0;
            } else if (size == 6) {
                tensor << A[0], A[5], A[4],
                          A[5], A[1], A[3],
                          A[4], A[3], A[2];
            } else if (size == 9) {
                tensor << A[0], A[3], A[6],
                          A[1], A[4], A[7],
                          A[2], A[5], A[8];
            } else {
                std::stringstream err_msg;
                err_msg << "Invalid flattened tensor size: " << size;
                throw RuntimeError(err_msg.str());
            }
            return tensor;
        }

        MeshPtr write_and_load(const std::string& filename, MeshPtr mesh,
                bool in_ascii=false) {