898 change test for valid transition distibution from ide model (#913)

Changed the index of a test in check_constraints for the ide model because the transitiondistribution S-> E is never used, so it does not have to have valid support. This can lead to unexpected errors if the function was set arbitrarily.

cpp/models/ide_secir/model.h

@@ -173,6 +173,8 @@ class Model
      * @param[in] idx_TransitionDistribution2 Specifies the index of the second relevant TransitionDistribution, 
      *              related to a flow from the considered #InfectionState to any other #InfectionState (in most cases to Recovered). 
      *              Necessary related probability is calculated via 1-probability[idx_TransitionDistribution1].
+     *              If the second index is not needed, eg if probability[idx_TransitionDistribution1]=1, 
+     *              just use an arbitrary legal index.
      * @param[in] dt Time discretization step size.
      */
     void compute_compartment(Eigen::Index idx_InfectionState, Eigen::Index idx_IncomingFlow,

cpp/models/ide_secir/parameters.h

@@ -269,10 +269,11 @@ class Parameters : public ParametersBase
                       1);
             return true;
         }
-
-        for (size_t i = 0; i < (int)InfectionTransition::Count; i++) {
+        /* The first entry of TransitionDistributions is not checked because the distribution S->E is never used 
+        (and it makes no sense to use the distribution). The support does not need to be valid.*/
+        for (size_t i = 1; i < (int)InfectionTransition::Count; i++) {
             if (floating_point_less(this->get<TransitionDistributions>()[i].get_support_max(10), 0.0, 1e-14)) {
-                log_error("Constraint check: One parameter in TransitionDistributions has invalid support.");
+                log_error("Constraint check: One function in TransitionDistributions has invalid support.");
                 return true;
             }
         }