# MB0048 : State the different types of models used in OR. Explain briefly the general methods for solving these OR models?

Posted October 3, 2011

on:**MB0048 : State the different types of models used in OR. Explain briefly the general methods for solving these OR models?**

**Answer: – **Types of OR Models

A model is an idealized representation or abstraction of a real-life system. The objective of a model is to identify significant factors that affect the real-life system and their interrelationships. A model aids the decision-making process as it provides a simplified description of complexities and uncertainties of a problem in a logical structure. The most significant advantage of a model is that it does not interfere with the real-life system.

**Classification of OR models**

You can broadly classify OR models into the following types.

a. **Physical Models** include all form of diagrams, graphs and charts. They are designed to tackle specific problems. They bring out significant factors and interrelationships in pictorial form to facilitate analysis. There are two types of physical models:

I. Iconic models

II. Analog models

Iconic models are primarily images of objects or systems, represented on a smaller scale. These models can simulate the actual performance of a product. Analog models are small physical systems having characteristics similar to the objects they represent, such as toys.

b. **Mathematical or Symbolic Models** employ a set of mathematical symbols to represent the decision variable of the system. The variables are related by mathematical systems. Some examples of mathematical models are allocation, sequencing, and replacement models.

c. **By nature of Environment:** Models can be further classified as follows:

I. Deterministic model in which everything is defined and the results are certain, such as an EOQ model.

II. Probabilistic Models in which the input and output variables follow a defined probability distribution, such as the Games Theory.

d. **By the extent of Generality** Models can be further classified as follows:

I. General Models are the models which you can apply in general to any problem. For example: Linear programming.

II. Specific Models on the other hand are models that you can apply only under specific conditions. For example: You can use the sales response curve or equation as a function of only in the marketing function.

General methods for solving these OR models

The basic dominant characteristic feature of operations research is that it employs mathematical representations or models to analyze problems. This distinct approach represents an adaptation of the scientific methodology used by the physical sciences. The scientific method translates a real given problem into a mathematical representation which is solved and retransformed into the original context. The OR approach to problem solving consists of the following steps: Defining the problem, Constructing the model, Solving the model, Validating the model and Implementing the final result.

**a) ****Definition**

The first and the most important step in the OR approach of problem solving is to define the problem. You need to ensure that the problem is identified properly because this problem statement will indicate three major aspects:

1) A description of the goal or the objective of the study

2) An identification of the decision alternative to the system

3) The recognition of the limitations, restrictions and requirements of the system.

**b) ****Construction**

Based on the problem definition, you need to identify and select the most appropriate model to represent the system. While selecting a model, you need to ensure that the model specifies quantitative expressions for the objective and the constraints of the problem in terms of its decision variables. A model gives a perspective picture of the whole problem and helps tackling it in a well-organized manner. Therefore, if the resulting model fits into one of the common mathematical models, you can obtain a convenient solution by using mathematical techniques. If the mathematical relationships of the model are too complex to allow analytic solutions, a simulation model may be more appropriate. There are various types of models which you can construct under different conditions.

**c) ****Solution**

After deciding on an appropriate model you need to develop a solution for the model and interpret the solution in the context of the given problem. A solution to a model implies determination of a specific set of decision variables that would yield an optimum solution. An optimum solution is one which maximizes or minimizes the performance of any measure in a model subject to the conditions and constraints imposed on the model.

**d) ****Validation**

A model is a good representation of a system. However, the optimal solution must work towards improving the system’s performance. You can test the validity of a model by comparing its performance with some past data available from the actual system. If under similar conditions of inputs, your model can reproduce the past performance of the system, then you can be sure that your model is valid. However, you will still have no assurance that future performance will continue to duplicate the past behavior. Secondly, since the model is based on careful examination of past data, the comparison should always reveal favorable results. In some instances, this problem may be overcome by using data from trial runs of the system. Note that such validation methods are not appropriate for non-existent systems, since data will not be available for comparison.

**e) ****Implementation**

You need to apply the optimal solution obtained from the model to the system and note the improvement in the performance of the system. You need to validate this performance check under changing conditions. To do so, you need to translate these results into detailed operating instructions issued in an understandable form to the individuals who will administer and operate the recommended system. The interaction between the operations research team and the operating personnel reaches its peak in this phase.

1 | Onah emmanuel

January 26, 2013 at 1:16 am

How can I get registered as a physics student?