conversion specializations

Author: SpectraL519

include/hgl/conversion.hpp

@@ -199,7 +199,33 @@ struct to_impl<impl::list_t<LayoutTag>, impl::flat_list_t<LayoutTag>> {
     }
 };
 
-// TODO: matrix <-> flat-matrix specializations
+// Conversion: matrix -> flat matrix (same layout)
+template <traits::c_hypergraph_layout_tag LayoutTag>
+requires traits::c_hypergraph_asymmetric_layout_tag<LayoutTag>
+struct to_impl<impl::flat_matrix_t<LayoutTag>, impl::matrix_t<LayoutTag>> {
+    template <typename TargetHypergraph, typename SourceHypergraph>
+    static void convert(TargetHypergraph& target, SourceHypergraph& source) {
+        target._impl._matrix =
+            decltype(target._impl._matrix)(std::views::as_rvalue(std::move(source._impl._matrix)));
+    }
+};
+
+// Conversion: flat matrix -> matrix (same layout)
+template <traits::c_hypergraph_layout_tag LayoutTag>
+requires traits::c_hypergraph_asymmetric_layout_tag<LayoutTag>
+struct to_impl<impl::matrix_t<LayoutTag>, impl::flat_matrix_t<LayoutTag>> {
+    template <typename TargetHypergraph, typename SourceHypergraph>
+    static void convert(TargetHypergraph& target, SourceHypergraph& source) {
+        auto& target_impl = target._impl;
+        auto& source_impl = source._impl;
+
+        target_impl._matrix_row_size = source_impl._matrix.n_cols();
+        target_impl._matrix.reserve(source_impl._matrix.n_rows());
+
+        for (const auto row : source_impl._matrix)
+            target_impl._matrix.emplace_back(row.begin(), row.end());
+    }
+};
 
 } // namespace detail