Page 1
Series Solution of Differential Equations
Institute of Lifelong Learning, University of Delhi pg. 1
Paper: Ordinary Differential Equations
Lesson: Series Solution of Differential Equation
Course Developer: Brijendra Yadav
Departmental / College: Department of Mathematics,
Acharya Narendra Dev College, University of Delhi
Page 2
Series Solution of Differential Equations
Institute of Lifelong Learning, University of Delhi pg. 1
Paper: Ordinary Differential Equations
Lesson: Series Solution of Differential Equation
Course Developer: Brijendra Yadav
Departmental / College: Department of Mathematics,
Acharya Narendra Dev College, University of Delhi
Series Solution of Differential Equations
Institute of Lifelong Learning, University of Delhi pg. 2
Table of Contents:
Chapter: Series Solutions of Differential Equations
1. Learning Outcomes
2. Introductions
3. Some basic definitions (power series, Analytic Function)
3.1 Power Series
3.2 Convergence of a power series
3.3 Analytic Function
3.4 Ordinary Point
3.5 Singular Point
3.6 Regular singular Point
3.7 Irregular singular Point
4. Power series salutation
4.1 The power series solution in powers of
0
() xx ?
4.2 Initial Value Problem
4.3 Frobeinus method
4.4 Indicial equation, Indicating the form of solutions
4.5 Frobenius method Unequal roots (not differing by an integer)
4.6 Frobenius method for double roots
4.7 Frobenius method Unequal roots (but solution is not linearly
independent)
Exercises
Summary
References
Page 3
Series Solution of Differential Equations
Institute of Lifelong Learning, University of Delhi pg. 1
Paper: Ordinary Differential Equations
Lesson: Series Solution of Differential Equation
Course Developer: Brijendra Yadav
Departmental / College: Department of Mathematics,
Acharya Narendra Dev College, University of Delhi
Series Solution of Differential Equations
Institute of Lifelong Learning, University of Delhi pg. 2
Table of Contents:
Chapter: Series Solutions of Differential Equations
1. Learning Outcomes
2. Introductions
3. Some basic definitions (power series, Analytic Function)
3.1 Power Series
3.2 Convergence of a power series
3.3 Analytic Function
3.4 Ordinary Point
3.5 Singular Point
3.6 Regular singular Point
3.7 Irregular singular Point
4. Power series salutation
4.1 The power series solution in powers of
0
() xx ?
4.2 Initial Value Problem
4.3 Frobeinus method
4.4 Indicial equation, Indicating the form of solutions
4.5 Frobenius method Unequal roots (not differing by an integer)
4.6 Frobenius method for double roots
4.7 Frobenius method Unequal roots (but solution is not linearly
independent)
Exercises
Summary
References
Series Solution of Differential Equations
Institute of Lifelong Learning, University of Delhi pg. 3
1. Learning outcomes : After reading this lesson, the read will be able
to understand
? Power series expansion about
0
xx ?
? Analytic nature of () Px and () Qx at
0
xx ?
? Nature of equations when
0
xx ? is an ordinary point
0
xx ? is a singular point
0
xx ? is a regular singular point
0
xx ? is a irregular singular point
? Solution of differential equation by Frobenius method.
? Forbenius method when 0 x ? is a regular singular point.
? Formation of indicial equation of differential equations.
? Power series solution when roots are distinct (Frobenius Method)
? Power series solution when roots are equal (Frobenius Method)
? Method of Power series solution when two solution (
1
() yx and
2
() yx ) are not linearly independent.
2. Introduction:
If a homogeneous linear differential equation has constant coefficients, it can
be solved by algebraic method, and its solutions are elementary functions,
known from calculus ( ,cos ,sin .)
x
e x xetc However, if such an equation has
variable coefficients (e.g., function ofx ), it must usually be solved by other
methods. Legendre’s equation
2
(1 ) " 2 ' ( 1) 0 x y xy n n y ? ? ? ? ? and Bessel’s
equation
2 2 2
( " ' ( ) 0) x y xy x n y ? ? ? ? are very important equations of this type.
These and other equations and their solution play a basic role in applied
mathematics. In this chapter we shall discuss the two standard methods of
solution and their applications: The power series method which fields
solutions in the form power series, and an extension of it, called the
Frobenius method.
Page 4
Series Solution of Differential Equations
Institute of Lifelong Learning, University of Delhi pg. 1
Paper: Ordinary Differential Equations
Lesson: Series Solution of Differential Equation
Course Developer: Brijendra Yadav
Departmental / College: Department of Mathematics,
Acharya Narendra Dev College, University of Delhi
Series Solution of Differential Equations
Institute of Lifelong Learning, University of Delhi pg. 2
Table of Contents:
Chapter: Series Solutions of Differential Equations
1. Learning Outcomes
2. Introductions
3. Some basic definitions (power series, Analytic Function)
3.1 Power Series
3.2 Convergence of a power series
3.3 Analytic Function
3.4 Ordinary Point
3.5 Singular Point
3.6 Regular singular Point
3.7 Irregular singular Point
4. Power series salutation
4.1 The power series solution in powers of
0
() xx ?
4.2 Initial Value Problem
4.3 Frobeinus method
4.4 Indicial equation, Indicating the form of solutions
4.5 Frobenius method Unequal roots (not differing by an integer)
4.6 Frobenius method for double roots
4.7 Frobenius method Unequal roots (but solution is not linearly
independent)
Exercises
Summary
References
Series Solution of Differential Equations
Institute of Lifelong Learning, University of Delhi pg. 3
1. Learning outcomes : After reading this lesson, the read will be able
to understand
? Power series expansion about
0
xx ?
? Analytic nature of () Px and () Qx at
0
xx ?
? Nature of equations when
0
xx ? is an ordinary point
0
xx ? is a singular point
0
xx ? is a regular singular point
0
xx ? is a irregular singular point
? Solution of differential equation by Frobenius method.
? Forbenius method when 0 x ? is a regular singular point.
? Formation of indicial equation of differential equations.
? Power series solution when roots are distinct (Frobenius Method)
? Power series solution when roots are equal (Frobenius Method)
? Method of Power series solution when two solution (
1
() yx and
2
() yx ) are not linearly independent.
2. Introduction:
If a homogeneous linear differential equation has constant coefficients, it can
be solved by algebraic method, and its solutions are elementary functions,
known from calculus ( ,cos ,sin .)
x
e x xetc However, if such an equation has
variable coefficients (e.g., function ofx ), it must usually be solved by other
methods. Legendre’s equation
2
(1 ) " 2 ' ( 1) 0 x y xy n n y ? ? ? ? ? and Bessel’s
equation
2 2 2
( " ' ( ) 0) x y xy x n y ? ? ? ? are very important equations of this type.
These and other equations and their solution play a basic role in applied
mathematics. In this chapter we shall discuss the two standard methods of
solution and their applications: The power series method which fields
solutions in the form power series, and an extension of it, called the
Frobenius method.
Series Solution of Differential Equations
Institute of Lifelong Learning, University of Delhi pg. 4
3. Some Basic Definitions:
3.1. Power Series:
The power series method is the standard basic method for solving linear
differential equations.
An infinite series of the form
2
0 0 1 0 2 0
0
( ) ( ) ( ) ...
n
n
n
c x x c c x x c x x
?
?
? ? ? ? ? ? ?
?
(1)
is called a power series in
0
( ), xx ? where
0 1 2 3
, , , ... c c c c are constants called
coefficients of the series and x is a variable.
In Particular, a Power series in x is an infinite series
23
0 1 2 3
0
...
n
n
n
c x c c x c x c x
?
?
? ? ? ? ?
?
(2)
For example the exponential function
x
e has the power series
2
345
0
1
1 ...
3! 4! 5!
! 2!
n
x
n
xx
x x x
ex
n
?
?
?
? ? ? ? ? ? ? ?
?
Similarly the other examples of the power series are
2
0
1
1 ..., 1
1
n
n
x x x x
x
?
?
? ? ? ? ? ?
?
?
(geometric series)
2 2 4
0
( 1)
cos 1 ...
(2 )! 2! 4!
nn
n
x x x
x
n
?
?
?
? ? ? ? ? ?
?
2 1 3 5
0
( 1)
sin ...
(2 1)! 3! 5!
nn
n
x x x
xx
n
? ?
?
?
? ? ? ? ? ?
?
?
Page 5
Series Solution of Differential Equations
Institute of Lifelong Learning, University of Delhi pg. 1
Paper: Ordinary Differential Equations
Lesson: Series Solution of Differential Equation
Course Developer: Brijendra Yadav
Departmental / College: Department of Mathematics,
Acharya Narendra Dev College, University of Delhi
Series Solution of Differential Equations
Institute of Lifelong Learning, University of Delhi pg. 2
Table of Contents:
Chapter: Series Solutions of Differential Equations
1. Learning Outcomes
2. Introductions
3. Some basic definitions (power series, Analytic Function)
3.1 Power Series
3.2 Convergence of a power series
3.3 Analytic Function
3.4 Ordinary Point
3.5 Singular Point
3.6 Regular singular Point
3.7 Irregular singular Point
4. Power series salutation
4.1 The power series solution in powers of
0
() xx ?
4.2 Initial Value Problem
4.3 Frobeinus method
4.4 Indicial equation, Indicating the form of solutions
4.5 Frobenius method Unequal roots (not differing by an integer)
4.6 Frobenius method for double roots
4.7 Frobenius method Unequal roots (but solution is not linearly
independent)
Exercises
Summary
References
Series Solution of Differential Equations
Institute of Lifelong Learning, University of Delhi pg. 3
1. Learning outcomes : After reading this lesson, the read will be able
to understand
? Power series expansion about
0
xx ?
? Analytic nature of () Px and () Qx at
0
xx ?
? Nature of equations when
0
xx ? is an ordinary point
0
xx ? is a singular point
0
xx ? is a regular singular point
0
xx ? is a irregular singular point
? Solution of differential equation by Frobenius method.
? Forbenius method when 0 x ? is a regular singular point.
? Formation of indicial equation of differential equations.
? Power series solution when roots are distinct (Frobenius Method)
? Power series solution when roots are equal (Frobenius Method)
? Method of Power series solution when two solution (
1
() yx and
2
() yx ) are not linearly independent.
2. Introduction:
If a homogeneous linear differential equation has constant coefficients, it can
be solved by algebraic method, and its solutions are elementary functions,
known from calculus ( ,cos ,sin .)
x
e x xetc However, if such an equation has
variable coefficients (e.g., function ofx ), it must usually be solved by other
methods. Legendre’s equation
2
(1 ) " 2 ' ( 1) 0 x y xy n n y ? ? ? ? ? and Bessel’s
equation
2 2 2
( " ' ( ) 0) x y xy x n y ? ? ? ? are very important equations of this type.
These and other equations and their solution play a basic role in applied
mathematics. In this chapter we shall discuss the two standard methods of
solution and their applications: The power series method which fields
solutions in the form power series, and an extension of it, called the
Frobenius method.
Series Solution of Differential Equations
Institute of Lifelong Learning, University of Delhi pg. 4
3. Some Basic Definitions:
3.1. Power Series:
The power series method is the standard basic method for solving linear
differential equations.
An infinite series of the form
2
0 0 1 0 2 0
0
( ) ( ) ( ) ...
n
n
n
c x x c c x x c x x
?
?
? ? ? ? ? ? ?
?
(1)
is called a power series in
0
( ), xx ? where
0 1 2 3
, , , ... c c c c are constants called
coefficients of the series and x is a variable.
In Particular, a Power series in x is an infinite series
23
0 1 2 3
0
...
n
n
n
c x c c x c x c x
?
?
? ? ? ? ?
?
(2)
For example the exponential function
x
e has the power series
2
345
0
1
1 ...
3! 4! 5!
! 2!
n
x
n
xx
x x x
ex
n
?
?
?
? ? ? ? ? ? ? ?
?
Similarly the other examples of the power series are
2
0
1
1 ..., 1
1
n
n
x x x x
x
?
?
? ? ? ? ? ?
?
?
(geometric series)
2 2 4
0
( 1)
cos 1 ...
(2 )! 2! 4!
nn
n
x x x
x
n
?
?
?
? ? ? ? ? ?
?
2 1 3 5
0
( 1)
sin ...
(2 1)! 3! 5!
nn
n
x x x
xx
n
? ?
?
?
? ? ? ? ? ?
?
?
Series Solution of Differential Equations
Institute of Lifelong Learning, University of Delhi pg. 5
3.2. Convergence of a power series:
The power series
2
0 0 1 0 2 0
0
( ) ( ) ( ) ...
n
n
n
c x x c c x x c x x
?
?
? ? ? ? ? ? ?
?
Converges (absolutely) for
0
x x R ??
where
1
lim ,
n
n
n
c
R
c
??
?
? provided the limit exits. (3)
R is called the radius of convergence of the power series (1) in the interval
( , ) RR ? which is said to be the interval of convergence.
If R ?? for a power series, then the interval of convergence of that power
series will be ( , ) ? ? ? i.e., the real line.
From the above condition we shall use the following results:
a. A power series represents a continuous function with its interval of
convergence
b. A power series can be differentiated term wise with in interval of
convergence.
3.3. Analytic Function:
A function () fx defined on an interval containing the point
0
xx ? is called
analytic at
0
x if its Taylor series
0
0
()
()
!
n
n
no
fx
xx
n
?
?
?
?
(4)
exists and converges to () fx for all x in the interval of convergence of ( 4 ).
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