feat(fem-and-beam-kernel): step 2 — beam-local-frame

include/fesa/fem/beam_frame.hpp

@@ -0,0 +1,32 @@
+#pragma once
+
+#include <array>
+#include <optional>
+#include <vector>
+
+#include <fesa/core/diagnostic.hpp>
+#include <fesa/core/vec3.hpp>
+
+namespace fesa {
+
+using Matrix12 = std::array<std::array<double, 12>, 12>;
+
+struct BeamFrame final {
+    Vec3 ex;
+    Vec3 ey;
+    Vec3 ez;
+};
+
+struct BeamFrameResult final {
+    std::optional<BeamFrame> frame;
+    std::vector<Diagnostic> diagnostics;
+};
+
+[[nodiscard]] BeamFrameResult make_beam_frame(
+    const Vec3& first,
+    const Vec3& second,
+    const Vec3& orientation);
+
+[[nodiscard]] Matrix12 beam_transformation(const BeamFrame& frame);
+
+}  // namespace fesa