Simulation and modeling - Old Questions

a. Queueing Discipline

Queue discipline refers to the rule that a server uses to choose the next customer from the queue when the server completes the service of the current customer. Common queue disciplines include first-in-first-out (FIFO); last-in-first-out (LIFO); service in random order (SIRO); shortest processing time first (SPT); and service according to priority (PR).

• First in first out :This principle states that customers are served one at a time and that the customer that has been waiting the longest is served first.
• Last in first out : This principle also serves customers one at a time, however the customer with the shortest waiting time will be served first. 
• Service in random order: A customer is picked up randomly from the waiting queue for service.
• Shortest job first: The next job to be served is the one with the smallest size (shortest service time).
• Priority: Customers with high priority are served first.

b. CSMP

CSMP or Continuous System Modelling Program is an early scientific computer software designed for modelling and solving differential equations numerically. This enables real-world systems to be simulated and tested with a computer.

Types of statements in CSMP:

1. Structural statements which defines the model. They consist of FORTARN like statement and functional block designed for operations that frequently occur in a model definition. Structural statement can make use of the operation of addition, subtraction, multiplication, division and exponentiation, using the same notation and rule as are used in FORTRAN. If the model include the equation .Then the following statement would be used

         X=6.0*Y/W+(Z-2)**2.0

2. Data statements which assign numerical value to parameters, constant and initial conditions. For example one data statement called INCON can be used to set the initial value of integration function block.

3. Control statements which specify options in the assembly and execution of program and choice of inputs. For e.g. If printed output is required, control statements with PRINT and PRDEL are used followed by the names of variables to form the outputs.