A pedagogical example
    
      - School model:
        
          - three-year third level school
 
          - interesting outputs
            
              - sizes xi(k) of class i
 
              - number of graduates xg(k)
 
            
           
          - all taken at the beginning of year k
 
          - three versions of growing complexity
 
        
       
      - Version A:
        
          - deterministic
            
              - constant fraction Ri of repeaters
 
              - constant fraction Di of dropouts 
 
            
           
          - non-integer sizes ("mean values")
 
          - exact definition
            
          
 
        
       
      - Version B:
        
          - non-deterministic, integer results
 
          - random number of repeaters ξR,i and
            dropouts ξD,i
 
          - given by binomial distribution B(n,p)
 
          - model equations change by
            
          
 
        
       
      - Version C:
        
          - add a fraction Mi of pupils, who downgrade
            at midterm
 
          - number of pupils again binomial
            
          
 
          - change from sample time 1 to mixed sample times!