From b9aacd9c2fdc61721c8ca3e1b40ebc92daa3772e Mon Sep 17 00:00:00 2001
From: "Claudius \"keldu\" Holeksa" <mail@keldu.de>
Date: Wed, 5 Nov 2025 13:38:04 +0100
Subject: Reworking structure

---
 lib/core/c++/equilibrium.hpp | 49 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)
 create mode 100644 lib/core/c++/equilibrium.hpp

(limited to 'lib/core/c++/equilibrium.hpp')

diff --git a/lib/core/c++/equilibrium.hpp b/lib/core/c++/equilibrium.hpp
new file mode 100644
index 0000000..bb55d00
--- /dev/null
+++ b/lib/core/c++/equilibrium.hpp
@@ -0,0 +1,49 @@
+#pragma once
+
+#include "descriptor.hpp"
+
+namespace kel {
+namespace lbm {
+template<typename T, typename Descriptor>
+saw::data<sch::FixedArray<T, Descriptor::Q>> equilibrium(saw::data<T> rho, saw::data<sch::FixedArray<T,Descriptor::D>> vel){
+	using dfi = df_info<T, Descriptor>;
+
+	saw::data<sch::FixedArray<T,Descriptor::Q>> eq;
+	//   ^
+	//  0.0
+	//  / \
+	//  | |
+	//
+	//  Velocity * Velocity meaning || vel ||_2^2 or <vel,vel>_2
+	saw::data<T> vel_vel{0.0};
+	for(uint64_t j = 0u; j < Descriptor::D; ++j){
+		vel_vel = vel_vel + vel.at(j) * vel.at(j);
+	}
+
+	/**
+	 * Calculate equilibrium
+	 */
+	for(uint64_t i = 0u; i < eq.template get_dim_size<0u>(); ++i){
+		saw::data<T> vel_c{};
+		for(uint64_t j = 0u; j < Descriptor::D; ++j){
+			// <vel,c_i>_2
+			vel_c = vel_c + (vel.at(j) * saw::data<T>{static_cast<saw::native_data_type<T>::type>(dfi::directions[i][j])});
+		}
+
+		auto vel_c_cs2 = vel_c * saw::data<T>{dfi::inv_cs2};
+
+		eq.at(i).set(
+			dfi::weights[i] * rho.get() * 
+			(
+			 1.0
+			 + vel_c_cs2.get()
+			 - dfi::inv_cs2 * 0.5 * vel_vel.get()
+			 + vel_c_cs2.get() * vel_c_cs2.get() * 0.5
+			)
+		);
+	}
+
+	return eq;
+}
+}
+}
-- 
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