Contents: Concept of Models Classification of Model Distribution-Lag Model Cobweb Model

1. Department of Computer Science and Engineering
Hamdard University Bangladesh
All Types of Models

2.  A Model is a representation and abstraction of anything such as a
real system, a proposed system, a futuristic system design, an
entity, a phenomenon, or an idea.
Concepts of Models

3. Models
Mathematical Physical
Dynamic Static Dynamic Static
Non-linear Linear Nonlinear Linear
Unstable
(Constrained)
Stable Unstable
(Nonexistent)
StableUnstable
(Explosive)
Stable
Computer
Dynamic Static
Classifications of Models

4.  Mathematical Model: is the one in which symbols and logic constitute the
model. The symbolism used can be a language or a mathematical notation.
 A simulation model is built in terms of logic and mathematical equations
and is an abstract model.
 Physical Model: Physical model is a smaller or larger physical copy of an
object. The object being modeled may be small (for example, an atom) or large
(for example, the Solar System).
 A model of an airplane (scaled down), a model of the atom (scaled up), a
map, a globe, a model car are examples of physical (iconic) models.
Mathematical Vs. Physical Models

5.  Static Model: is the one which describes relationships that do not change with
respect to time.
 An architectural model of a house is a static physical model.
 An equation relating the lengths and weights on each side of a
playground variation is a static mathematical model.
 Static computer model which means fixed.
 Dynamic Model: is the one which describes time-varying
relationships.
 A wind tunnel is a dynamic physical model.
 The equations of motion of the planets around the sun constitute a
dynamic mathematical model of the solar system.
 Dynamic computer usually means capable of action and/or change.
Static Vs. Dynamic (Abstract /Physical/Computer) Models

6.  Analytical Model: is the one which is solved by using the deductive reasoning of
mathematical theory.
 A Linear Programming model, a Mixed Integer Linear Programming
model, a nonlinear optimization model are examples of analytical
models.
 Numerical Model: is the one which is solved by applying
computational procedures.
 Finding the roots of a nonlinear algebraic equation, f(x) = 0, using the
numerical model.
Analytical Vs. Numerical Mathematical Models

7.  Linear Model: is the one which describes relationships in linear
form.
 The equation 3x + 4z + 1=0 is a linear model.
 Nonlinear Model: is the one which describes relationships in
nonlinear form.
 The equation 2𝑥2 + 𝑦3—2=0 is a nonlinear model.
Linear Vs. Nonlinear Mathematical Models

8.  Stable Model: is the one which tends to return to its initial condition
after being disturbed.
 Like a simple pendulum.
 Unstable Model: is the one which may or may not come back to its
initial condition after being disturbed.
Stable Or Unstable Mathematical Models

9.  Steady-State Model: is the one whose behavior in one time period is
of the same nature as any other period.
 Transient Model: is the one whose behavior changes with respect to
time.
time
Transient Behavior Steady-State Behavior
Steady-state Or Transient Mathematical Models
state

10.  Descriptive Model: a system that represent a relationship but does not
indicate any course of action.
 The equation F (force) = M (mass) x A (acceleration) is a descriptive
model.
 All simulation models are descriptive models.
 Prescriptive or Normative Model: a system in that it prescribes the course
of action that the decision maker should take to achieve a defined objective.
 Decision analysis models are prescriptive.
Descriptive Vs. Prescriptive (Normative) Models

12.  If the regression model includes not only the current but
also the lagged (past) values of the explanatory variables
(the X’s) it is called a distributed-lag model.
 If the model includes one or more lagged values of the
dependent variable among its explanatory variables, it is
called an autoregressive model. This model is know as a
dynamic model.
Distributed-lag Model

13. Cobweb Model
 It is an economic model.
 In the model of supply and demand, the price adjusts so that the quantity
supplied and quantity demand are equal.
 The equilibrium is not always clear, so that some slopes are unstable.

14. Thats All !
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