first try

Processes/CMakeLists.txt

@@ -10,6 +10,7 @@ endif (PYTHIA8_FOUND)
 add_subdirectory (HadronicElasticModel)
 add_subdirectory (UrQMD)
 add_subdirectory (SwitchProcess)
+add_subdirectory (VerySimpleModel)
 
 # continuous physics
 add_subdirectory (EnergyLoss)
@@ -34,3 +35,4 @@ add_dependencies(CORSIKAprocesses ProcessTrackingLine)
 add_dependencies(CORSIKAprocesses ProcessEnergyLoss)
 add_dependencies(CORSIKAprocesses ProcessUrQMD)
 add_dependencies(CORSIKAprocesses ProcessParticleCut)
+add_dependencies(CORSIKAprocesses ProcessVerySimpleModel)

Processes/VerySimpleModel/CMakeLists.txt

+set (
+  MODEL_SOURCES
+  VerySimpleModel.cc
+  )
+
+set (
+  MODEL_HEADERS
+  VerySimpleModel.h
+  )
+
+set (
+  MODEL_NAMESPACE
+  corsika/process/very_simple_model
+  )
+
+add_library (ProcessVerySimpleModel STATIC ${MODEL_SOURCES})
+CORSIKA_COPY_HEADERS_TO_NAMESPACE (ProcessVerySimpleModel ${MODEL_NAMESPACE} ${MODEL_HEADERS})
+
+set_target_properties (
+  ProcessVerySimpleModel
+  PROPERTIES
+  VERSION ${PROJECT_VERSION}
+  SOVERSION 1
+#  PUBLIC_HEADER "${MODEL_HEADERS}"
+  )
+
+# target dependencies on other libraries (also the header onlys)
+target_link_libraries (
+  ProcessVerySimpleModel
+  CORSIKAunits
+  CORSIKAgeometry
+  CORSIKAsetup
+  )
+
+target_include_directories (
+  ProcessVerySimpleModel 
+  INTERFACE 
+  $<BUILD_INTERFACE:${PROJECT_BINARY_DIR}/include>
+  $<INSTALL_INTERFACE:include/include>
+  )
+
+install (
+  TARGETS ProcessVerySimpleModel
+  LIBRARY DESTINATION lib
+  ARCHIVE DESTINATION lib
+#  PUBLIC_HEADER DESTINATION include/${MODEL_NAMESPACE}
+  )
+
+
+# --------------------
+# code unit testing
+#~ CORSIKA_ADD_TEST (testProcessVerySimpleModel)
+#~ target_link_libraries (
+  #~ testProcessVerySimpleModel
+  #~ ProcessVerySimpleModel
+  #~ CORSIKAsetup
+  #~ CORSIKAgeometry
+  #~ CORSIKAunits
+  #~ CORSIKAtesting
+  #~ )

Processes/VerySimpleModel/VerySimpleModel.cc

+/*
+ * (c) Copyright 2018 CORSIKA Project, corsika-project@lists.kit.edu
+ *
+ * See file AUTHORS for a list of contributors.
+ *
+ * This software is distributed under the terms of the GNU General Public
+ * Licence version 3 (GPL Version 3). See file LICENSE for a full version of
+ * the license.
+ */
+
+#include <corsika/process/very_simple_model/VerySimpleModel.h>
+#include <corsika/setup/SetupStack.h>
+#include <corsika/setup/SetupTrajectory.h>
+
+#include <tuple>
+
+using namespace corsika;
+using namespace corsika::units::si;
+using namespace corsika::process::very_simple_model;
+
+using SetupParticle = corsika::setup::Stack::StackIterator;
+using SetupProjectile = corsika::setup::StackView::StackIterator;
+
+  void VerySimpleModel::Init() {}
+
+  VerySimpleModel::VerySimpleModel() {}
+
+  template <>
+  process::EProcessReturn VerySimpleModel::DoInteraction(SetupProjectile& vP) {
+    const auto projectileID = vP.GetPID();
+
+    auto const posOrig = vP.GetPosition();
+    auto const tOrig = vP.GetTime();
+    auto const eProjectileLab = vP.GetEnergy();
+    auto const pProjectileLab = vP.GetMomentum();
+
+    const auto* currentNode = vP.GetNode();
+    const auto& mediumComposition =
+        currentNode->GetModelProperties().GetNuclearComposition();
+
+    // get cross sections for target materials
+    auto const& compVec = mediumComposition.GetComponents();
+    std::vector<units::si::CrossSectionType> cross_section_of_components(compVec.size());
+
+    for (size_t i = 0; i < compVec.size(); ++i) {
+      cross_section_of_components[i] = GetCrossSection(projectileID, compVec[i]);
+    }
+
+    const auto corsikaTargetId =
+        mediumComposition.SampleTarget(cross_section_of_components, fRNG);
+
+    // add secondaries to corsika stack
+    auto const sec1Code = particles::Code::MuPlus;
+    auto const sec1E = eProjectileLab;
+    auto const sec1P = pProjectileLab;
+
+    auto secondary1 = vP.AddSecondary(
+        std::tuple<particles::Code, units::si::HEPEnergyType, stack::MomentumVector,
+              geometry::Point, units::si::TimeType>(sec1Code, sec1E, sec1P, posOrig,
+                                                    tOrig));
+
+    auto const sec2Code = particles::Code::MuMinus;
+    auto const sec2E = eProjectileLab;
+    auto const sec2P = pProjectileLab;
+    
+    auto secondary2 = vP.AddSecondary(
+        std::tuple<particles::Code, units::si::HEPEnergyType, stack::MomentumVector,
+              geometry::Point, units::si::TimeType>(sec2Code, sec2E, sec2E, posOrig,
+                                                    tOrig));
+
+    return process::EProcessReturn::eOk;
+  }
+
+  template <>
+  corsika::units::si::CrossSectionType GetCrossSection(SetupParticle const& vProjectile,
+                                                       particles::Code vTargetCode) {
+    if (vProjectile.GetPID() == particles::MuPlus) {
+      return 20_mb;
+    } else if (vProjectile.GetPID() == particles::MuMinus) {
+      return 10_mb;
+    } else {
+      return 0_mb;
+    }
+  }
+
+  template <>
+  corsika::units::si::GrammageType GetInteractionLength(Projectile const& vP) {
+    auto const* currentNode = vP.GetNode();
+    const auto& mediumComposition =
+        currentNode->GetModelProperties().GetNuclearComposition();
+
+    si::CrossSectionType weightedProdCrossSection = mediumComposition.WeightedSum(
+        [=](particles::Code targetID) -> si::CrossSectionType {
+          return this->GetCrossSection(corsikaBeamId, targetID);
+        });
+
+    GrammageType const int_length = mediumComposition.GetAverageMassNumber() *
+                                    units::constants::u / weightedProdCrossSection;
+
+    return int_length;
+  }

Processes/VerySimpleModel/VerySimpleModel.h

+/*
+ * (c) Copyright 2018 CORSIKA Project, corsika-project@lists.kit.edu
+ *
+ * See file AUTHORS for a list of contributors.
+ *
+ * This software is distributed under the terms of the GNU General Public
+ * Licence version 3 (GPL Version 3). See file LICENSE for a full version of
+ * the license.
+ */
+
+#ifndef _Physics_VerySimpleModel_h_
+#define _Physics_VerySimpleModel_h_
+
+#include <corsika/particles/ParticleProperties.h>
+#include <corsika/process/InteractionProcess.h>
+#include <corsika/units/PhysicalUnits.h>
+#include <corsika/random/RNGManager.h>
+
+namespace corsika::process::very_simple_model {
+
+  class VerySimpleModel : public corsika::process::InteractionProcess<VerySimpleModel> {
+    corsika::random::RNG& fRNG =
+        corsika::random::RNGManager::GetInstance().GetRandomStream("VerySimpleModel");
+
+  public:
+    VerySimpleModel();
+
+    void Init();
+
+    template <typename TParticle>
+    corsika::units::si::CrossSectionType GetCrossSection(TParticle const&,
+                                                         particles::Code);
+
+    template <typename TParticle>
+    corsika::units::si::GrammageType GetInteractionLength(TParticle const&);
+
+    template <typename TProjectile>
+    corsika::process::EProcessReturn DoInteraction(TProjectile&);
+  };
+
+} // namespace corsika::process::very_simple_model
+
+#endif