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Intro ODE

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INTRODUCTION TO

DIFFERENTIAL EQUATIONS

Dr . Imam Jauhari Maknun, S.T. M.T., MSc.


OUTLINE

1. Definitions and Terminology

2. Initial-Value Problems

3. Differential Equations as Mathematical Models


Definitions and Terminology
Introduction
The words differential and equation certainly suggest
solving some kind of equation that contains
derivatives.

But before you start solving anything, you must learn


some of the basic definitions and terminology of the
subject
Definition
The derivative dy/dx of a function y = ϕ (x) is itself another
function ϕ '(x) found by an appropriate rule.
For example, the function is differentiable on
the interval (- ∞, ∞), and its derivative is
If we replace in the last equation by the symbol
y, we obtain
Classification by Type
If a differential equation contains only ordinary derivatives of
one or more functions with respect to a single independent
variable it is said to be an ordinary differential equation
(ODE).
Classification by Type
An equation involving only partial derivatives of
one or more functions of two or more independent
variables is called a partial differential equation
(PDE).
Notation
Throughout this text, ordinary derivatives will be written
using either the Leibniz notation dy/dx, d2y/dx2, d3y/dx3, • •
• , or the prime notation y', y", y"', ....
Classification by Order
The order of a differential equation (ODE or PDE) is the order
of the highest derivative in the equation.
The differential equations

are examples of a second-order ordinary differential equation


and a fourth-order partial differential equation, respectively.
Classification by Linearity
 The equations

are, in turn, examples of linear first-, second-, and third-order


ordinary differential equations.
 The equations

are examples of nonlinear first-, second-, and fourth-order ordinary


differential equations, respectively
Solution
Explicit and Implicit Solutions
 You should be familiar with the terms explicit and implicit
functions from your study of calculus.
 A solution in which the dependent variable is expressed
solely in terms of the independent variable and constants
is said to be an explicit solution.
Systems of Differential Equations
 Up to this point we have been discussing single differential
equations containing one unknown function.

 But often in theory, as well as in many applications, we must


deal with systems of differential equations
Initial-Value Problems
Initial-Value Problem
We are often interested in problems in which we seek a
solution y(x) of a differential equation so that y(x) satisfies
prescribed side conditions-that is, conditions that are
imposed on the unknown y(x) or on its derivatives
Differential Equations as
Mathematical Models
Mathematical Models
Steps in the modeling process
Mathematical Models

Mixing tank Water draining from a tank Position of rock measured


from ground level
Mathematical Models

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