From c3ccb9a09c18d31f7c708efaef3790d1303c6bf4 Mon Sep 17 00:00:00 2001
From: Jean-Marco Alameddine <jean-marco.alameddine@udo.edu>
Date: Fri, 20 Jan 2023 15:56:28 +0100
Subject: [PATCH 1/2] Add GEOMETRY_PRECISION when approaching border to avoid
 getting stuck in front of it

---
 src/PROPOSAL/detail/PROPOSAL/Propagator.cxx | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/PROPOSAL/detail/PROPOSAL/Propagator.cxx b/src/PROPOSAL/detail/PROPOSAL/Propagator.cxx
index 37929328d..e19c4d804 100644
--- a/src/PROPOSAL/detail/PROPOSAL/Propagator.cxx
+++ b/src/PROPOSAL/detail/PROPOSAL/Propagator.cxx
@@ -252,6 +252,7 @@ int Propagator::AdvanceParticle(ParticleState &state,
             // reached geometry border
             advancement_type = ReachedBorder;
             distance = distance_to_border;
+            distance += GEOMETRY_PRECISION; // avoid particles getting stuck in front of border
         } else {
             // iteration not finished! discard energy and grammage
             advancement_type = InvalidStep;

From 3277618b129262be2365a0a3425eba35aed4b390 Mon Sep 17 00:00:00 2001
From: Jean-Marco Alameddine <jean-marco.alameddine@udo.edu>
Date: Fri, 20 Jan 2023 16:45:28 +0100
Subject: [PATCH 2/2] Add test of Propagator including a medium transition in
 air

---
 tests/Propagator_TEST.cxx | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/tests/Propagator_TEST.cxx b/tests/Propagator_TEST.cxx
index e72726cb7..22be518d8 100644
--- a/tests/Propagator_TEST.cxx
+++ b/tests/Propagator_TEST.cxx
@@ -57,6 +57,45 @@ TEST(Propagator, min_energy)
     }
 }
 
+TEST(Propagator, BorderTransition)
+{
+    auto p_def = MuMinusDef();
+    auto medium = Air();
+    auto cuts = std::make_shared<EnergyCutSettings>(INF, 0.05, false);
+    auto cross = GetStdCrossSections(p_def, medium, cuts, true);
+
+    auto collection = PropagationUtility::Collection();
+    collection.interaction_calc = make_interaction(cross, true);
+    collection.displacement_calc = make_displacement(cross, true);
+    collection.time_calc = make_time(cross, p_def, true);
+    collection.scattering = make_scattering(MultipleScatteringType::Highland, {}, p_def, medium);
+
+    auto prop_utility = PropagationUtility(collection);
+
+    auto density_distr = std::make_shared<Density_homogeneous>(medium);
+    auto sphere1 = std::make_shared<Sphere>(Cartesian3D(0, 0, -637218600), 1e20, 637413400);
+    sphere1->SetHierarchy(1);
+    auto sphere2 = std::make_shared<Sphere>(Cartesian3D(0, 0, -637218600), 637413400, 0);
+    sphere2->SetHierarchy(2);
+
+    auto sector1 = std::make_tuple(sphere1, prop_utility, density_distr);
+    auto sector2 = std::make_tuple(sphere2, prop_utility, density_distr);
+
+    std::vector<Sector> sec_vec = {sector1, sector2};
+
+    auto prop = Propagator(p_def, sec_vec);
+
+    auto init_state = ParticleState();
+    init_state.energy = 1e9;
+    init_state.position = Cartesian3D(0, 0, 1.01948e+07);
+    init_state.direction = Cartesian3D(0, 0, -1);
+
+    for (size_t i=0; i<1000; i++) {
+        std::cout << i << std::endl;
+        auto sec = prop.Propagate(init_state);
+    }
+}
+
 int main(int argc, char** argv)
 {
     ::testing::InitGoogleTest(&argc, argv);