check that threshold is high enough for pythia in EAS simulation

applications/c8_air_shower.cpp

@@ -416,6 +416,13 @@ int main(int argc, char** argv) {
   // have SIBYLL always for PROPOSAL photo-hadronic interactions
   auto sibyll = std::make_shared<corsika::sibyll::Interaction>(all_elements);
 
+  // energy threshold for high energy hadronic model. Affects LE/HE switch for
+  // hadron interactions and the hadronic photon model in proposal
+  // valid range varies a bit between models. pythia only has cross sections tabulated
+  // down to 100GeV.
+  HEPEnergyType const heHadronModelThreshold =
+      1_GeV * app["--hadronModelTransitionEnergy"]->as<double>();
+
   if (auto const modelStr = app["--hadronModel"]->as<std::string>();
       modelStr == "SIBYLL-2.3d") {
     heModel = DynamicInteractionProcess<StackType>{sibyll};
@@ -428,6 +435,11 @@ int main(int argc, char** argv) {
   } else if (modelStr == "Pythia8") {
     heModel = DynamicInteractionProcess<StackType>{
         std::make_shared<corsika::pythia8::Interaction>()};
+    if (heHadronModelThreshold < 100_GeV) {
+      CORSIKA_LOG_CRITICAL(
+          "threshold too low for Pythia! use --hadronModelTransitionEnergy>=100_GeV!");
+      return EXIT_FAILURE;
+    }
   } else {
     CORSIKA_LOG_CRITICAL("invalid choice \"{}\"; also check argument parser", modelStr);
     return EXIT_FAILURE;
@@ -471,11 +483,6 @@ int main(int argc, char** argv) {
   set_energy_production_threshold(Code::TauMinus, std::min({emcut, hadcut, mucut}));
   set_energy_production_threshold(Code::TauPlus, std::min({emcut, hadcut, mucut}));
 
-  // energy threshold for high energy hadronic model. Affects LE/HE switch for
-  // hadron interactions and the hadronic photon model in proposal
-  HEPEnergyType const heHadronModelThreshold =
-      1_GeV * app["--hadronModelTransitionEnergy"]->as<double>();
-
   corsika::proposal::Interaction emCascade(
       env, sophia, sibyll->getHadronInteractionModel(), heHadronModelThreshold);