added a comment

Author: lenaploetzke

cpp/models/ide_secir/model.cpp

@@ -99,13 +99,18 @@ void Model::initialize(ScalarType dt)
             m_populations[Eigen::Index(0)][Eigen::Index(InfectionState::Dead)];
     }
     else {
-
         // compute Susceptibles at time 0  and m_forceofinfection at time -dt as initial values for discretization scheme
         // use m_forceofinfection at -dt to be consistent with further calculations of S (see compute_susceptibles()),
         // where also the value of m_forceofinfection for the previous timestep is used
         update_forceofinfection(dt, true);
         if (m_forceofinfection > 1e-12) {
             m_initialization_method = 4;
+
+            /* Attention: With an inappropriate combination of parameters and initial conditions, it can happen that S 
+            becomes greater than N when this formula is used. In this case, at least one compartment is initialized 
+            with a number less than zero, so that a log_error is thrown.
+            However, this initialization method is consistent with the numerical solver of the model equations,
+            so it may sometimes make sense to use this method. */
             m_populations[Eigen::Index(0)][Eigen::Index(InfectionState::Susceptible)] =
                 m_transitions.get_last_value()[Eigen::Index(InfectionTransition::SusceptibleToExposed)] /
                 (dt * m_forceofinfection);