Creating a Basic Cohort Model

Abstract

In this chapter our main aim is to introduce you to the Modgen software and to the Visual Studio programming software, guiding you through the creation of a first basic model. This model will be based on one single type of event: death. Although this will yield only a small number of results, such as life expectancy at birth, it will allow us to demonstrate and to practise the use of several of the basic ideas in Modgen. We will move on to the calculation and presentation of other elements of the life table in the next chapter.

Appendices

Appendices

1.1.1 Appendix 1.1 ModgenExample.mpp

Code Sections: Header (lines 1 to 24), CaseSimulation() Function (lines 25 to 62), Simulation() Function (lines 63 to 97)

1  //LABEL(ModgenExample, EN) Core simulation functions 2 3  /* NOTE(ModgenExample, EN) 4     This module contains core simulation functions and definitions. 5  */ 6 7   // The model version number 8   version 1, 0, 0, 0; 9 10  // The model type 11  model_type case_based; 12 13  // The data type used to represent time 14  time_type double; 15 16  // Supported languages 17  languages { 18      EN // English 19  }; 20 21  // The CaseSimulation function simulates a single case, 22  // and is called by the Simulation function declared later 23  // in this module. 24 25  void CaseSimulation( ) 26  { 27      // Initialize the first actor in the case. 28      Person *poFirstActor = new Person(); 29      poFirstActor->Start( ); 30 31      // Continue processing events until there are no more. 32      // Model code is responsible for ending the case by calling 33      // Finish on all existant actors. 34 35      // The Modgen run-time implements 36      // the global event queue gpoEventQueue. 37      while ( !gpoEventQueue->Empty() ) 38      { 39          // The global variables gbCancelled and gbErrors 40          // are maintained by the Modgen run-time. 41          if ( gbCancelled || gbErrors ) 42          { 43              // The user cancelled the simulation, 44              // or run-time errors occurred. 45              // Terminate the case immediately. 46              gpoEventQueue->FinishAllActors(); 47          } 48          else 49          { 50              // Age all actors to the time of the next event. 51              gpoEventQueue->WaitUntil( gpoEventQueue->NextEvent() ); 52     53              // Implement the next event. 54              gpoEventQueue->Implement(); 55          } 56      } 57 58      // Note that Modgen handles memory cleanup 59      // when Finish is called on an actor. 60  } 61 62 63  // The Simulation function is called by Modgen to simulate a set of cases. 64  void Simulation() 65  { 66      // counter for cases simulated 67      long lCase = 0; 68 69      // The Modgen run-time implements CASES (used below), 70      // which supplies the number of cases to simulate 71      // in a particular thread. 72      // 73      // The following loop for cases is stopped if 74      // - the simulation is cancelled by the user, 75      // with partial reports (gbInterrupted) 76      // - the simulation is cancelled by the user, 77      // with no partial reports (gbCancelled) 78      // - a run-time error occurs (gbErrors) 79      // 80      // The global variables gbInterrupted, gbCancelled and gbErrors 81      // are maintained by the Modgen run-time. 82      for ( lCase = 0; lCase < CASES() && !gbInterrupted && !gbCancelled 83          && !gbErrors; lCase++ ) 84      { 85          // Simulate a case. 86 87          // Tell the Modgen run-time to prepare to simulate a new case. 88          StartCase(); 89 90          // Call the CaseSimulation function 91          // defined earlier in this module. 92          CaseSimulation(); 93 94          // Tell the Modgen run-time that the case has been completed. 95          SignalCase(); 96      } 97  }

1.1.2 Appendix 1.2 PersonCore.mpp

Code Sections: Header, Parameters, Actor Person and functions, Tables

1   //LABEL(PersonCore, EN) Core functionality of the Person actor 2 3   /* NOTE(PersonCore, EN) 4       This module contains the basic information which defines 5       the Person case. 6   */ 7 8   parameters 9   { 10      //EN Annual hazard of death 11      double MortalityHazard; 12      /* NOTE(MortalityHazard, EN) 13          A constant hazard of death results in an exponential 14          survival function. 15      */ 16  }; 17 18  actor Person     //EN Individual 19 { 20      // The variables time and age are automatically defined by Modgen. 21      // Model-specific labels and notes are supplied below. 22 23      //LABEL(Person.time, EN) Time 24      /*NOTE(Person.time, EN) 25          Time is a continuous quantity in this model. 26          A unit of time is a year. 27      */ 28 29      //LABEL(Person.age, EN) Age 30      /*NOTE(Person.age, EN) 31          Age is a continuous quantity in this model. 32          A unit of age is a year. 33      */ 34 35      //EN Alive 36         ogical alive = {TRUE}; 37      /*NOTE(Person.alive, EN) 38          Set to TRUE when the actor starts, and to FALSE just 39          before the actor finishes. Since the numeric value 40          of TRUE is 1 and FALSE is 0, this variable 41          can also be used to count actors in tables. 42      */ 43 44      event timeMortalityEvent, MortalityEvent; //EN Mortality event 45 46      //LABEL(Person.Start, EN) Starts the actor 47      void Start(); 48 49      //LABEL(Person.Finish, EN) Finishes the actor 50      void Finish(); 51  }; 52 53  /*NOTE(Person.MortalityEvent, EN) 54      This event implements a constant hazard of death. 55  */ 56 57  // The time function of MortalityEvent 58  TIME Person::timeMortalityEvent() 59  { 60      TIME tEventTime = TIME_INFINITE; 61 62      // Draw a random waiting time to death 63      // from an exponential distribution 64      // based on the constant hazard MortalityHazard. 65      tEventTime = WAIT( - TIME( log( RandUniform(1) ) / 66          MortalityHazard ) ); 67 68      return tEventTime; 69 } 70 71  // The implement function of MortalityEvent 72  void Person::MortalityEvent() 73  { 74      alive = FALSE; 75 76      // Remove the actor from the simulation. 77      Finish(); 78  } 79 80  /*NOTE(Person.Start, EN) 81      The Start function initializes actor variables before simulation 82      of the actor commences. 83  */ 84  void Person::Start() 85  { 86      // Modgen initializes all actor variables 87      // before the code in this function is executed. 88 89      age = 0; 90      time = 0; 91 92      // After the code in this function is executed, 93      // Modgen initializes events and tables for the actor. 94      // Modgen also outputs starting values to the 95      // tracking file if requested. 96  } 97 98 /*NOTE(Person.Finish, EN) 99      The Finish function terminates the simulation of an actor. 100  */ 101  void Person::Finish() 102  { 103      // After the code in this function is executed, 104      // Modgen removes the actor from tables and from the simulation. 105      // Modgen also recuperates any memory used by the actor. 106  } 107 108  /*NOTE(DurationOfLife, EN) 109      This table contains statistics related to the duration of life. 110  */ 111  table Person DurationOfLife //EN Duration of Life 112  { 113      { 114          //EN Population size 115          value_in(alive), 116          //EN Minimum duration of life decimals=4 117          min_value_out(duration()), 118          //EN Maximum duration of life decimals=4 119          max_value_out(duration()), 120          //EN Life expectancy decimals=4 121          duration() / value_in(alive) 122 123      }   //EN Demographic characteristics 124  };