feat(fem-and-beam-kernel): step 0 — quadrature-and-shape-functions

include/fesa/fem/gauss_rule.hpp

@@ -0,0 +1,14 @@
+#pragma once
+
+#include <span>
+
+namespace fesa {
+
+struct GaussPoint1D final {
+    double xi;
+    double weight;
+};
+
+[[nodiscard]] std::span<const GaussPoint1D> gauss_rule_1d(int order);
+
+}  // namespace fesa

include/fesa/fem/line2_shape.hpp

@@ -0,0 +1,13 @@
+#pragma once
+
+#include <array>
+
+namespace fesa {
+
+[[nodiscard]] std::array<double, 2> line2_shape(double xi);
+
+[[nodiscard]] std::array<double, 2> line2_shape_derivative(double xi);
+
+[[nodiscard]] double line2_jacobian(double length);
+
+}  // namespace fesa