feat(equation-and-linear-solve): step 0 — symmetric-csr-assembly

include/fesa/assembly/equation_system.hpp

@@ -0,0 +1,14 @@
+#pragma once
+
+#include <vector>
+
+#include <fesa/assembly/symmetric_csr.hpp>
+
+namespace fesa {
+
+struct EquationSystem final {
+    SymmetricCsr stiffness;
+    std::vector<double> force;
+};
+
+}  // namespace fesa

include/fesa/assembly/serial_assembler.hpp

@@ -0,0 +1,13 @@
+#pragma once
+
+#include <fesa/assembly/equation_system.hpp>
+#include <fesa/fem/dof_manager.hpp>
+#include <fesa/model/domain.hpp>
+
+namespace fesa {
+
+[[nodiscard]] EquationSystem assemble_serial(
+    const Domain& domain,
+    const DofManager& dofs);
+
+}  // namespace fesa

include/fesa/assembly/symmetric_csr.hpp

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+#include <vector>
+
+namespace fesa {
+
+// Zero-based CSR containing only the upper triangle. Column indices are
+// strictly increasing within each row.
+struct SymmetricCsr final {
+    std::size_t order;
+    std::vector<std::int32_t> row_offsets;
+    std::vector<std::int32_t> column_indices;
+    std::vector<double> values;
+};
+
+}  // namespace fesa

include/fesa/fem/dof_manager.hpp

@@ -34,13 +34,13 @@ public:
     [[nodiscard]] std::size_t free_equation_count() const noexcept;
     [[nodiscard]] std::optional<std::size_t> equation(
         DofAddress address) const;
+    [[nodiscard]] std::size_t full_dof(DofAddress address) const;
     [[nodiscard]] std::array<std::size_t, 12> element_full_dofs(
         const BeamElement& element) const;
     [[nodiscard]] std::vector<double> reconstruct_full(
         std::span<const double> reduced) const;
 
 private:
-    [[nodiscard]] std::size_t full_dof(DofAddress address) const;
     [[nodiscard]] std::size_t node_full_dof_base(NodeId node) const;
 
     std::map<std::int64_t, std::size_t> node_full_dof_bases_;

include/fesa/model/domain.hpp

@@ -57,6 +57,8 @@ public:
 
     [[nodiscard]] const Node& node(NodeId id) const;
     [[nodiscard]] const Node& node(const EntityOrigin& origin) const;
+    [[nodiscard]] const IsotropicElastic& material(MaterialId id) const;
+    [[nodiscard]] const BeamSection& section(SectionId id) const;
 
 private:
     friend class DomainBuilder;