1 files changed, 54 insertions, 0 deletions
diff --git a/lib/core/c++/momentum_gather.hpp b/lib/core/c++/momentum_gather.hpp
new file mode 100644
index 0000000..7b1fc96
--- /dev/null
+++ b/lib/core/c++/momentum_gather.hpp
@@ -0,0 +1,54 @@
+#pragma once
+
+#include "common.hpp"
+#include "macroscopic.hpp"
+#include "component.hpp"
+#include "equilibrium.hpp"
+
+namespace kel {
+namespace lbm {
+namespace cmpt {
+// Gather the force, Luke!
+struct ForceGather {};
+}
+
+template<typename T, typename Descriptor, typename Encode>
+class component<T,Descriptor,cmpt::ForceGather, Encode> {
+private:
+public:
+	template<typename CellFieldSchema, typename MacroFieldSchema>
+	void apply(const saw::data<CellFieldSchema, Encode>& field, const saw::data<MacroFieldSchema,Encode>& macros,
+		saw::data<sch::FixedArray<sch::UInt64,Descriptor::D>> index, saw::data<sch::UInt64> time_step) const {
+
+		using dfi = df_info<T,Descriptor>;
+		bool is_even = ((time_step.get() % 2) == 0);
+
+		auto& dfs_old_f = (is_even) ? field.template get<"dfs_old">() : field.template get<"dfs">();
+
+		auto& porous_f = macros.template get<"porosity">();
+		auto& porous = porous_f.at(index);
+
+		auto& force_f = macros.template get<"force">();
+		auto& force = force_f.at(index);
+
+		for(uint64_t k{0u}; k < Descriptor::D; ++k){
+			force.at({{k}}).set(0);
+		}
+
+		auto& dfs = dfs_old_f.at(index);
+		for(uint64_t i{0u}; i < Descriptor::Q; ++i){
+			uint64_t i_opp = dfi::opposite_index[i];
+			auto dfs_diff = dfs.at({i}) - dfs.at({i_opp});
+			for(uint64_t k{0u}; k < Descriptor::D; ++k){
+				force.at({{k}}) = force.at({{k}}) + dfs_diff * saw::data<T>{dfi::directions[i][k]};
+			}
+		}
+
+		saw::data<sch::Scalar<T>> one;
+		one.at({}) = 1.0;
+		auto flip_porous = one - porous;
+		force = force * flip_porous;
+	}
+};
+}
+}