5 files changed, 92 insertions, 7 deletions

diff --git a/lib/core/c++/fplbm.hpp b/lib/core/c++/fplbm.hpp
index 61def6b..c974472 100644
--- a/lib/core/c++/fplbm.hpp
+++ b/lib/core/c++/fplbm.hpp
@@ -114,6 +114,19 @@ public:
 		auto& vel_f = macros.template get<"velocity">();
 		auto& por_f = macros.template get<"porosity">();
 
+		// Temporary find a better way
+		auto& force_f = macros.template get<"force">();
+
+
+		/**
+		 * The other methods all work with a flipped porosity.
+		 * For compat reasons this is also flipped
+		 */
+		auto porosity = por_f.at(index);
+		saw::data<sch::Scalar<T>> one;
+		one.at({}) = 1.0;
+		auto flip_porosity = one - porosity;
+
 		saw::data<sch::Scalar<T>>& rho = rho_f.at(index);
 
 		saw::data<sch::Scalar<T>> half;
@@ -128,12 +141,13 @@ public:
 		saw::data<sch::Scalar<T>> min_two;
 		min_two.at({}).set(-2);
 
-		auto force = vel * rho * min_two * por_f.at(index);
+		// Maybe ? 
+		auto& force = force_f.at(index);
+		force = vel * rho * min_two * flip_porosity;
 
 		saw::data<sch::Scalar<T>> dfi_inv_cs2;
 		dfi_inv_cs2.at({}).set(dfi::inv_cs2);
 
-
 		// auto vel = vel_f.at(index);
 
 		for(uint64_t i = 0u; i < Descriptor::Q; ++i){
diff --git a/lib/core/c++/lbm.hpp b/lib/core/c++/lbm.hpp
index b34ec10..23d30b1 100644
--- a/lib/core/c++/lbm.hpp
+++ b/lib/core/c++/lbm.hpp
@@ -16,6 +16,7 @@
 #include "iterator.hpp"
 #include "hlbm.hpp"
 #include "macroscopic.hpp"
+#include "momentum_gather.hpp"
 #include "memory.hpp"
 #include "psm.hpp"
 #include "stream.hpp"
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;
+	}
+};
+}
+}
diff --git a/lib/core/c++/particle/porosity.hpp b/lib/core/c++/particle/porosity.hpp
index 11185c5..2f39d2e 100644
--- a/lib/core/c++/particle/porosity.hpp
+++ b/lib/core/c++/particle/porosity.hpp
@@ -48,17 +48,17 @@ public:
 		auto rad_high = rad + eps_h;
 
 		if(s_dist.at({}) <= rad_low.at({})){
-			por.at({}).set(1);
+			por.at({}).set(0);
 			return por;
 		}
 		if(s_dist.at({}) >= rad_high.at({})){
-			por.at({}).set(0);
+			por.at({}).set(1);
 			return por;
 		}
 
 		{
-			typename saw::native_data_type<T>::type inner = (std::numbers::pi / ( eps.at({}).get() )) * (s_dist - rad_low).at({}).get();
-			auto cos_inner = std::cos(inner);
+			typename saw::native_data_type<T>::type inner = (std::numbers::pi / ( 2 * eps.at({}).get() )) * (s_dist - rad_low).at({}).get();
+			auto cos_inner = std::sin(inner);
 			auto cos_i_2 = cos_inner * cos_inner;
 			por.at({}).set(cos_i_2);
 		}
diff --git a/lib/core/c++/psm.hpp b/lib/core/c++/psm.hpp
index 3bd3520..6dc146f 100644
--- a/lib/core/c++/psm.hpp
+++ b/lib/core/c++/psm.hpp
@@ -40,7 +40,7 @@ public:
 
 		auto& rho_f = macros.template get<"density">();
 		auto& vel_f = macros.template get<"velocity">();
-	
+		
 		saw::data<sch::Scalar<T>>& rho = rho_f.at(index);
 		saw::data<sch::Vector<T,Descriptor::D>>& vel = vel_f.at(index);
 
@@ -60,6 +60,22 @@ public:
 			uint64_t i_opp = dfi::opposite_index[i];
 			dfs.at({i}) = dfs_cpy.at({i}) + frequency_ * (eq.at(i) - dfs_cpy.at({i})) * porous.at({}) + (dfs_cpy.at({i_opp}) - dfs_cpy.at({i}) ) * flip_porous;
 		}
+
+		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);
+		}
+
+		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;
+			}
+		}
+
+		force = force * porous;
 	}
 };