From 4fab8965692f75fea3cbbabb3381bfeb00511669 Mon Sep 17 00:00:00 2001
From: "Claudius \"keldu\" Holeksa" <mail@keldu.de>
Date: Sun, 5 Jul 2026 22:13:52 +0200
Subject: Found c++ magic

---
 examples/stokes_drag_particle_2d_hlbm_gpu/sim.cpp | 2 ++
 modules/core/c++/hlbm.hpp                         | 5 +++--
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/examples/stokes_drag_particle_2d_hlbm_gpu/sim.cpp b/examples/stokes_drag_particle_2d_hlbm_gpu/sim.cpp
index a919bbe..49e6d43 100644
--- a/examples/stokes_drag_particle_2d_hlbm_gpu/sim.cpp
+++ b/examples/stokes_drag_particle_2d_hlbm_gpu/sim.cpp
@@ -197,6 +197,7 @@ saw::error_or<void> step(
 	q.submit([&](acpp::sycl::handler& h){
 		component<T,Desc,cmpt::BGK, encode::Sycl<saw::encode::Native>> bgk{0.8};
 		component<T,Desc,cmpt::Hlbm,encode::Sycl<saw::encode::Native>> collision{0.8};
+		component<T,Desc,cmpt::HlbmOneParticleMomentumExchange,encode::Sycl<saw::encode::Native>> one_part_moment;
 		component<T,Desc,cmpt::BounceBack,encode::Sycl<saw::encode::Native>> bb;
 		component<T,Desc,cmpt::AntiBounceBack<0u>,encode::Sycl<saw::encode::Native>> abb;
 
@@ -241,6 +242,7 @@ saw::error_or<void> step(
 				break;
 				case 2u:
 					opa.apply(macros,index,t_i);
+					one_part_moment.apply(fields,macros,index,t_i);
 					collision.apply(fields,macros,index,t_i);
 					fg.apply(fields,macros,index,t_i);
 					break;
diff --git a/modules/core/c++/hlbm.hpp b/modules/core/c++/hlbm.hpp
index 677d37a..346ec04 100644
--- a/modules/core/c++/hlbm.hpp
+++ b/modules/core/c++/hlbm.hpp
@@ -156,8 +156,9 @@ template<typename T, typename Desc, typename Encode>
 class component<T, Desc, cmpt::HlbmOneParticleMomentumExchange, Encode> final {
 public:
 	template<typename CellFieldSchema, typename MacroFieldSchema, typename ParticleSchema>
-	void apply(const saw::data<CellFieldSchema, Encode>& field, const saw::data<MacroFieldSchema,Encode>& macros, const saw::data<ParticleSchema,Encode>& part_group, saw::data<sch::FixedArray<sch::UInt64,1u>> index, saw::data<sch::UInt64> time_step) const {
+	void apply(const saw::data<CellFieldSchema, Encode>& field, const saw::data<MacroFieldSchema,Encode>& macros, saw::data<sch::FixedArray<sch::UInt64,Desc::D>> index, saw::data<sch::UInt64> time_step) const {
 		//
+		using dfi = df_info<T,Desc>;
 		bool is_even = ((time_step.get() % 2) == 0);
 		
 		auto& dfs_old_f = (is_even) ? field.template get<"dfs_old">() : field.template get<"dfs">();
@@ -177,7 +178,7 @@ public:
 		auto& force_f = macros.template get<"force">();
 		
 		// Set Force
-		force.at(index) = momentum * macros.template get<"density">().at(index);
+		force_f.at(index) = momentum * macros.template get<"porosity">().at(index);
 	}
 };
 }
-- 
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