Eigen Value And Eigen
Vector
GUIDED BY: MANSI K. DESAI
Group Members:-
SR NO. NAME ENROLLMENT NUMBER
1. RANA PAYAL MAHESHBHAI 151100106072
2. PATEL RUTVIJ GANESHBHAI 151100106073
3. SAVALIYAAKSHAY JAYANTILAL 151100106074
4. TANDEL PAYALBENVITHTHALBHAI 151100106075
5. TANDEL SNEHAL MAHENDRABHAI 151100106076
6. VAGHELA SAHIL PREMJIBHAI 151100106077
7. EHSANULLAHAYDIN 151100106078
8. SHUAIB KOHEE 151100106079
9. WAHEDULLAH EHSAS 151100106080
Eigenvalues and Eigenvectors
• If A is an n x n matrix and λ is a scalar for which Ax = λx has a nontrivial
solution x ∈ ℜⁿ, then λ is an eigenvalue of A and x is a corresponding
eigenvector of A.
– Ax=λx=λIx
– (A-λI)x=0
• The matrix (A-λI ) is called the characteristic matrix of a where I is the
Unit matrix.
–
• The equation det (A-λI )= 0 is called characteristic equation of A and the
roots of this equation are called the eigenvalues of the matrix A.The set
of all eigenvectors is called the eigenspace of A corresponding to λ.The
set of all eigenvalues of a is called spectrum of A.
Characteristic Equation
▪ If A is any square matrix of order n, we can form the matrix , where
is the nth order unit matrix.
▪ The determinant of this matrix equated to zero,
▪ i.e.,
is called the characteristic equation of A.
0
λa...aa
............
a...λaa
a...aλa
λA
nnn2n1
2n2221
1n1211




 I
• On expanding the determinant, we get
• where k’s are expressible in terms of the elements a
•The roots of this equation are called Characteristic roots
or latent roots or eigen values of the matrix A.
•X = is called an eigen vector or latent vector
0k...λkλkλ1)( n
2n
2
1n
1
nn
 
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2
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...
x
x
x
Properties of Eigen Values:-
1. The sum of the eigen values of a matrix is the sum of the
elements of the principal diagonal.
2.The product of the eigen values of a matrix A is equal to its
determinant.
3. If is an eigen value of a matrix A, then 1/ is the eigen value
of A-1 .
4.If is an eigen value of an orthogonal matrix, then 1/ is also its
eigen value.

PROPERTY 1:- If λ1, λ2,…, λn are the eigen values of A, then
i. k λ1, k λ2,…,k λn are the eigen values of the matrix kA,
where k is a non – zero scalar.
ii. are the eigen values of the inverse
matrix A-1.
iii. are the eigen values of Ap, where p is any positive
integer.
Algebraic & Geometric Multiplicity
▪ If the eigenvalue λ of the equation det(A-λI)=0 is repeated n times
then n is called the algebraic multiplicity of λ.The number of linearly
independent eigenvectors is the difference between the number of
unknowns and the rank of the corresponding matrix A- λI and is
known as geometric multiplicity of eigenvalue λ.
Cayley-Hamilton Theorem:-
• Every square matrix satisfies its own characteristic equation.
• Let A = [aij]n×n be a square matrix then,
nnnn2n1n
n22221
n11211
a...aa
................
a...aa
a...aa
A
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
Let the characteristic polynomial of A be 
(λ)
Then,
The characteristic equation is
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11 12 1n
21 22 2n
n1 n2 nn
φ(λ) = A - λI
a - λ a ... a
a a - λ ... a
=
... ... ... ...
a a ... a - λ
| A - λI|=0
 n n-1 n-2
0 1 2 n
n n-1 n-2
0 1 2 n
We are to prove that
p λ +p λ +p λ +...+p = 0
p A +p A +p A +...+p I= 0 ...(1)
Note 1:- Premultiplying equation (1) by A-1 , we
have
I

n-1 n-2 n-3 -1
0 1 2 n-1 n
-1 n-1 n-2 n-3
0 1 2 n-1
n
0 =p A +p A +p A +...+p +p A
1
A =- [p A +p A +p A +...+p I]
p
This result gives the inverse of A in terms of (n-1) powers of A
and is considered as a practical method for the computation of the
inverse of the large matrices.
Note 2:- If m is a positive integer such that m > n then any positive
integral power Am of A is linearly expressible in terms of those of
lower degree.
Example 1:-
Verify Cayley – Hamilton theorem for the matrix
A = . Hence compute A-1 .
Solution:-The characteristic equation of A is
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2
AAA
A
To verify Cayley – Hamilton theorem, we have to
show that A3 – 6A2 +9A – 4I = 0 … (1)
Now,
A3 -6A2 +9A – 4I = 0
= -6 + 9
-4
=
This verifies Cayley – Hamilton theorem.
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Now, pre – multiplying both sides of (1) by A-1 , we have
A2 – 6A +9I – 4 A-1 = 0
=> 4 A-1 = A2 – 6 A +9I
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Example 2:-
Given find Adj A by using Cayley –
Hamilton theorem.
Solution:- The characteristic equation of the given matrix
A is
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A
tion)simplifica(on035λ3λλor
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i.e.,0λIA
23

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By Cayley – Hamilton theorem, A should satisfy
A3 – 3A2 + 5A + 3I = 0
Pre – multiplying by A-1 , we get
A2 – 3A +5I +3A-1 = 0
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Similarity of Matrix
▪ IfA & B are two square matrices of order n then B is said to be similar
to A, if there exists a non-singular matrix P such that,
B= P-1AP
1. Similarity matrices is an equivalence relation.
2. Similarity matrices have the same determinant.
3. Similar matrices have the same characteristic polynomial and
hence the same eigenvalues. If x is an eigenvector corresponding to
the eigenvalue λ, then P-1x is an eigenvector of B corresponding to
the eigenvalue λ where B= P-1AP.
Diagonalization
▪ A matrix A is said to be diagonalizable if it is similar to diagonal
matrix.
▪ A matrix A is diagonalizable if there exists an invertible matrix P such
that P-1AP=D where D is a diagonal matrix, also known as spectral
matrix.The matrix P is then said to diagonalize A of transform A to
diagonal form and is known as modal matrix.
Reduction of a matrix to Diagonal Form
▪ If a square matrix A of order n has n linearly independent eigen
vectors then a matrix B can be found such that B-1AB is a diagonal
matrix.
▪ Note:-The matrix B which diagonalises A is called the modal matrix
of A and is obtained by grouping the eigen vectors ofA into a square
matrix.
Example:-
Reduce the matrix A = to diagonal form by
similarity transformation. Hence find A3.
Solution:- Characteristic equation is
=> λ = 1, 2, 3
Hence eigenvalues of A are 1, 2, 3.
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1λ-20
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vector then 
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AMM 1
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=> A = MDM-1
A2 = (MDM-1) (MDM-1)
= MD2M-1 [since M-1M = I]
Similarly, A3 = MD3M-1
=
A3 =
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19-80
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311
Orthogonally Similar Matrices
▪ If A & B are two square matrices of order n then B is said to be orthogonally
similar to A, if there exists orthogonal matrix P such that
B= P-1AP
Since P is orthogonal,
P-1=PT
B= P-1AP=PTAP
1. A real symmetric of order n has n mutually orthogonal real eigenvectors.
2. Any two eigenvectors corresponding to two distinct eigenvalues of a real
symmetric matrix are orthogonal.
Diagonalises the matrix A = by means of an
orthogonal transformation.
Solution:-
Characteristic equation of A is
32
Example :-
204
060
402
66,2,λ
0λ)16(6λ)λ)(2λ)(6(2
0
λ204
0λ60
40λ2

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I
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1
1 2
3
1
1
2
3
1 3
2
1 3
1 1 2 3 1
1 1
x
when λ = -2,let X = x be the eigen vector
x
then (A + 2 )X = 0
4 0 4 x 0
0 8 0 x = 0
4 0 4 x 0
4x + 4x = 0 ...(1)
8x = 0 ...(2)
4x + 4x = 0 ...(3)
x = k , x = 0, x = -k
1
X = k 0
-1
2
2I
0
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 
  
     
     
     
          
 

1
2
3
1
2
3
1 3
1 3
1 3 2
2 2 3
x
whenλ = 6,let X = x betheeigenvector
x
then (A - 6 )X = 0
-4 0 4 x 0
0 0 x = 0
4 0 -4 x 0
4x + 4x = 0
4x - 4x = 0
x = x and x isarbitrary
x must be so chosen that X and X are orthogonal among th
.1
emselves
and also each is orthogonal with X
   
   
   
      


 
 
 
  

2 3
3 1
3 2
3
1 α
Let X = 0 and let X = β
1 γ
Since X is orthogonal to X
α - γ = 0 ...(4)
X is orthogonal to X
α + γ = 0 ...(5)
Solving (4)and(5), we get α = γ = 0 and β is arbitrary.
0
Taking β = 1, X = 1
0
1 1 0
Modal matrix is M = 0 0 1
-1 1
 
 
 
  0
 
 
 
 
 
 
  
 
  
    
    
    
        
    
 
 
 
  
The normalised modal matrix is
1 1
0
2 2
N = 0 0 1
1 1
- 0
2 2
1 1
0 - 1 1
02 2 2 0 4 2 2
1 1
D = N'AN = 0 0 6 0 0 0 1
2 2
4 0 2 1 1
- 00 1 0
2 2
-2 0 0
D = 0 6 0 which is the required diagonal matrix
0 0 6
.
Quadratic Forms
DEFINITION:-
A homogeneous polynomial of second degree in any number of
variables is called a quadratic form.
For example,
ax2 + 2hxy +by2
ax2 + by2 + cz2 + 2hxy + 2gyz + 2fzx and
ax2 + by2 + cz2 + dw2 +2hxy +2gyz + 2fzx + 2lxw + 2myw + 2nzw
are quadratic forms in two, three and four variables
In n – variables x1,x2,…,xn, the general quadratic form
is
In the expansion, the co-efficient of xixj = (bij + bji).
38
 

n
1j
n
1i
jiijjiij bbwhere,xxb
).b(b
2
1
awherexxaxxb
baandaawherebb2aSuppose
jiijijji
n
1j
n
1i
ijji
n
1j
n
1i
ij
iiiijiijijijij


   
Hence every quadratic form can be written as
   
getweform,matrixin
formsquadraticofexamplessaidabovethewritingNow
.x,...,x,xXandaAwhere
symmetric,alwaysisAmatrixthethatso
AX,X'xxa
n21ij
ji
n
1j
n
1i
ij

 













y
x
bh
ha
y][xby2hxyax(i) 22
 
 















































w
z
y
x
dnml
ncgf
mgbh
lfha
wzyx
2nzw2myw2lxwzx2f2gyz2hxydw2czbyax(iii)
z
y
x
cgf
gbh
fha
zyx2fzx2gyz2hxyczbyax(ii)
222
222
Two Theorems On Quadratic Form
Theorem(1): A quadratic form can always be expressed with respect to
a given coordinate system as
where A is a unique symmetric matrix.
Theorem2: Two symmetric matrices A and B represent the same
quadratic form if and only if
B=PTAP
where P is a non-singular matrix.
AxxY T

Nature of Quadratic Form
A real quadratic form X’AX in n variables is said to be
i. Positive definite if all the eigen values ofA > 0.
ii. Negative definite if all the eigen values of A < 0.
iii. Positive semi definite if all the eigen values ofA 0 and at least one
eigen value = 0.
iv. Negative semi definite if all the eigen values of
A 0 and at least one eigen value = 0.
v. Indefinite if some of the eigen values ofA are + ve and others – ve.
Find the nature of the following quadratic forms
i. x2 + 5y2 + z2 + 2xy + 2yz + 6zx
ii. 3x2 + 5y2 + 3z2 – 2yz + 2zx – 2xy
Solution:-
i. The matrix of the quadratic form is
43
Example :-











113
151
311
A
The eigen values of A are -2, 3, 6.
Two of these eigen values being positive and one being
negative, the given quadratric form is indefinite.
ii. The matrix of the quadratic form is
The eigen values of A are 2, 3, 6. All these eigen values being
positive, the given quadratic form is positive definite.














311
151
113
A
Linear Transformation of a Quadratic
Form
▪ Let X’AX be a quadratic form in n- variables and let X = PY ….. (1)
where P is a non – singular matrix, be the non – singular
transformation.
▪ From (1), X’ = (PY)’ =Y’P’ and hence
X’AX =Y’P’APY =Y’(P’AP)Y
=Y’BY …. (2)
where B = P’AP.
Therefore,Y’BY is also a quadratic form in n- variables. Hence it
is a linear transformation of the quadratic form X’AX under the
linear transformation X = PY and B = P’AP.
Note. (i) Here B = (P’AP)’ = P’AP = B
(ii) ρ(B) = ρ(A)
Therefore, A and B are congruent matrices.
Reduce 3x2 + 3z2 + 4xy + 8xz + 8yz into canonical form.
Or
Diagonalises the quadratic form 3x2 + 3z2 + 4xy + 8xz + 8yz by
linear transformations and write the linear transformation.
Or
Reduce the quadratic form 3x2 + 3z2 + 4xy + 8xz + 8yz into the
sum of squares.
47
Example:-
Solution:- The given quadratic form can be written as X’AX where
X = [x, y, z]’ and the symmetric matrix
A =
Let us reduce A into diagonal matrix. We know tat A = I3AI3.










344
402
423









































100
010
001
344
402
423
100
010
001
344
402
423
 

   
   
    
           
      
    
   
21 31OperatingR ( 2 / 3),R ( 4 / 3)
(for A onL.H.S.andpre factor on R.H.S.), we get
3 2 4 1 0 0
1 0 0
4 4 2
0 1 0 A 0 1 0
3 3 3
0 0 1
4 7 4
0 0 1
3 3 3





















































100
010
3
4
3
2
1
A
10
3
4
01
3
2
001
3
7
3
4
0
3
4
3
4
0
423
getweR.H.S),onfactorpostandL.H.S.onA(for
4/3)(C2/3),(COperating 3121







































100
010
3
4
3
2
1
A
112
01
3
2
001
100
3
4
3
4
0
003
getwe(1),ROperating 32
APP'1,
3
4
3,Diagor
100
110
2
3
2
1
A
112
01
3
2
001
100
0
3
4
0
003
getwe(1),COperating 32














































The canonical form of the given quadratic form is
Here ρ(A) = 3, index = 1, signature = 1 – (2) = -1.
Note:- In this problem the non-singular transformation which
reduces the given quadratic form into the canonical form is X = PY.
i.e.,
 
2
3
2
2
2
1
3
2
1
321
yy
3
4
3y
y
y
y
100
0
3
4
0
003
yyyAP)Y(P'Y'































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
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



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
















3
2
1
112
01
3
2
001
y
y
y
z
y
x
Thank you 

Eigen value and eigen vector

  • 1.
    Eigen Value AndEigen Vector GUIDED BY: MANSI K. DESAI
  • 2.
    Group Members:- SR NO.NAME ENROLLMENT NUMBER 1. RANA PAYAL MAHESHBHAI 151100106072 2. PATEL RUTVIJ GANESHBHAI 151100106073 3. SAVALIYAAKSHAY JAYANTILAL 151100106074 4. TANDEL PAYALBENVITHTHALBHAI 151100106075 5. TANDEL SNEHAL MAHENDRABHAI 151100106076 6. VAGHELA SAHIL PREMJIBHAI 151100106077 7. EHSANULLAHAYDIN 151100106078 8. SHUAIB KOHEE 151100106079 9. WAHEDULLAH EHSAS 151100106080
  • 3.
    Eigenvalues and Eigenvectors •If A is an n x n matrix and λ is a scalar for which Ax = λx has a nontrivial solution x ∈ ℜⁿ, then λ is an eigenvalue of A and x is a corresponding eigenvector of A. – Ax=λx=λIx – (A-λI)x=0 • The matrix (A-λI ) is called the characteristic matrix of a where I is the Unit matrix. – • The equation det (A-λI )= 0 is called characteristic equation of A and the roots of this equation are called the eigenvalues of the matrix A.The set of all eigenvectors is called the eigenspace of A corresponding to λ.The set of all eigenvalues of a is called spectrum of A.
  • 4.
    Characteristic Equation ▪ IfA is any square matrix of order n, we can form the matrix , where is the nth order unit matrix. ▪ The determinant of this matrix equated to zero, ▪ i.e., is called the characteristic equation of A. 0 λa...aa ............ a...λaa a...aλa λA nnn2n1 2n2221 1n1211      I
  • 5.
    • On expandingthe determinant, we get • where k’s are expressible in terms of the elements a •The roots of this equation are called Characteristic roots or latent roots or eigen values of the matrix A. •X = is called an eigen vector or latent vector 0k...λkλkλ1)( n 2n 2 1n 1 nn               4 2 1 ... x x x
  • 6.
    Properties of EigenValues:- 1. The sum of the eigen values of a matrix is the sum of the elements of the principal diagonal. 2.The product of the eigen values of a matrix A is equal to its determinant. 3. If is an eigen value of a matrix A, then 1/ is the eigen value of A-1 . 4.If is an eigen value of an orthogonal matrix, then 1/ is also its eigen value. 
  • 7.
    PROPERTY 1:- Ifλ1, λ2,…, λn are the eigen values of A, then i. k λ1, k λ2,…,k λn are the eigen values of the matrix kA, where k is a non – zero scalar. ii. are the eigen values of the inverse matrix A-1. iii. are the eigen values of Ap, where p is any positive integer.
  • 8.
    Algebraic & GeometricMultiplicity ▪ If the eigenvalue λ of the equation det(A-λI)=0 is repeated n times then n is called the algebraic multiplicity of λ.The number of linearly independent eigenvectors is the difference between the number of unknowns and the rank of the corresponding matrix A- λI and is known as geometric multiplicity of eigenvalue λ.
  • 9.
    Cayley-Hamilton Theorem:- • Everysquare matrix satisfies its own characteristic equation. • Let A = [aij]n×n be a square matrix then, nnnn2n1n n22221 n11211 a...aa ................ a...aa a...aa A              
  • 10.
    Let the characteristicpolynomial of A be  (λ) Then, The characteristic equation is             11 12 1n 21 22 2n n1 n2 nn φ(λ) = A - λI a - λ a ... a a a - λ ... a = ... ... ... ... a a ... a - λ | A - λI|=0
  • 11.
     n n-1n-2 0 1 2 n n n-1 n-2 0 1 2 n We are to prove that p λ +p λ +p λ +...+p = 0 p A +p A +p A +...+p I= 0 ...(1) Note 1:- Premultiplying equation (1) by A-1 , we have I  n-1 n-2 n-3 -1 0 1 2 n-1 n -1 n-1 n-2 n-3 0 1 2 n-1 n 0 =p A +p A +p A +...+p +p A 1 A =- [p A +p A +p A +...+p I] p
  • 12.
    This result givesthe inverse of A in terms of (n-1) powers of A and is considered as a practical method for the computation of the inverse of the large matrices. Note 2:- If m is a positive integer such that m > n then any positive integral power Am of A is linearly expressible in terms of those of lower degree.
  • 13.
    Example 1:- Verify Cayley– Hamilton theorem for the matrix A = . Hence compute A-1 . Solution:-The characteristic equation of A is              211 121 112 tion)simplifica(on049λ6λλor 0 λ211 1λ21 11λ2 i.e.,0λIA 23      
  • 14.
  • 15.
    A3 -6A2 +9A– 4I = 0 = -6 + 9 -4 = This verifies Cayley – Hamilton theorem.              222121 212221 212222              655 565 556              211 121 112           100 010 001 0 000 000 000           
  • 16.
    Now, pre –multiplying both sides of (1) by A-1 , we have A2 – 6A +9I – 4 A-1 = 0 => 4 A-1 = A2 – 6 A +9I                                                                    311 131 113 4 1 311 131 113 100 010 001 9 211 121 112 6 655 565 556 4 1 1 A A
  • 17.
    Example 2:- Given findAdj A by using Cayley – Hamilton theorem. Solution:- The characteristic equation of the given matrix A is               113 110 121 A tion)simplifica(on035λ3λλor 0 λ113 1λ10 1-2λ1 i.e.,0λIA 23      
  • 18.
    By Cayley –Hamilton theorem, A should satisfy A3 – 3A2 + 5A + 3I = 0 Pre – multiplying by A-1 , we get A2 – 3A +5I +3A-1 = 0                                                         339 330 363 3A 146 223 452 113 110 121 113 110 121 A.AANow, (1)...5I)3A(A 3 1 A 2 21-
  • 19.
  • 20.
  • 21.
    Similarity of Matrix ▪IfA & B are two square matrices of order n then B is said to be similar to A, if there exists a non-singular matrix P such that, B= P-1AP 1. Similarity matrices is an equivalence relation. 2. Similarity matrices have the same determinant. 3. Similar matrices have the same characteristic polynomial and hence the same eigenvalues. If x is an eigenvector corresponding to the eigenvalue λ, then P-1x is an eigenvector of B corresponding to the eigenvalue λ where B= P-1AP.
  • 22.
    Diagonalization ▪ A matrixA is said to be diagonalizable if it is similar to diagonal matrix. ▪ A matrix A is diagonalizable if there exists an invertible matrix P such that P-1AP=D where D is a diagonal matrix, also known as spectral matrix.The matrix P is then said to diagonalize A of transform A to diagonal form and is known as modal matrix.
  • 23.
    Reduction of amatrix to Diagonal Form ▪ If a square matrix A of order n has n linearly independent eigen vectors then a matrix B can be found such that B-1AB is a diagonal matrix. ▪ Note:-The matrix B which diagonalises A is called the modal matrix of A and is obtained by grouping the eigen vectors ofA into a square matrix.
  • 24.
    Example:- Reduce the matrixA = to diagonal form by similarity transformation. Hence find A3. Solution:- Characteristic equation is => λ = 1, 2, 3 Hence eigenvalues of A are 1, 2, 3.             300 120 211 0             λ-300 1λ-20 21λ1-
  • 25.
    Corresponding to λ= 1, let X1 = be the eigen vector then           3 2 1 x x x                                                  0 0 1 kX x0x,kx 02x 0xx 02xx 0 0 0 x x x 200 110 210 0X)I(A 11 3211 3 32 32 3 2 1 1
  • 26.
    Corresponding to λ= 2, let X2 = be the eigen vector then,           3 2 1 x x x                                                  0 1- 1 kX x-kx,kx 0x 0x 02xxx 0 0 0 x x x 100 100 211- 0X)(A 22 32221 3 3 321 3 2 1 2 0, I2
  • 27.
    Corresponding to λ= 3, let X3 = be the eigen vector then,           3 2 1 x x x                                                  2 2- 3 kX xk-x,kx 0x 02xxx 0 0 0 x x x 000 11-0 212- 0X)(A 33 13332 3 321 3 2 1 3 3 2 2 3 , 2 I3 k x
  • 28.
    Hence modal matrixis                                         2 1 00 11-0 2 1- 11 M MAdj. M 1-00 220 122- MAdj. 2M 200 21-0 311 M 1
  • 29.
  • 30.
    Similarly, A3 =MD3M-1 = A3 =                                                2700 19-80 327-1 2 1 00 11-0 2 1 11 2700 080 001 200 21-0 311
  • 31.
    Orthogonally Similar Matrices ▪If A & B are two square matrices of order n then B is said to be orthogonally similar to A, if there exists orthogonal matrix P such that B= P-1AP Since P is orthogonal, P-1=PT B= P-1AP=PTAP 1. A real symmetric of order n has n mutually orthogonal real eigenvectors. 2. Any two eigenvectors corresponding to two distinct eigenvalues of a real symmetric matrix are orthogonal.
  • 32.
    Diagonalises the matrixA = by means of an orthogonal transformation. Solution:- Characteristic equation of A is 32 Example :- 204 060 402 66,2,λ 0λ)16(6λ)λ)(2λ)(6(2 0 λ204 0λ60 40λ2      
  • 33.
    I                                                 1 1 2 3 1 1 2 3 1 3 2 1 3 1 1 2 3 1 1 1 x when λ = -2,let X = x be the eigen vector x then (A + 2 )X = 0 4 0 4 x 0 0 8 0 x = 0 4 0 4 x 0 4x + 4x = 0 ...(1) 8x = 0 ...(2) 4x + 4x = 0 ...(3) x = k , x = 0, x = -k 1 X = k 0 -1
  • 34.
    2 2I 0                                         1 2 3 1 2 3 1 3 1 3 1 3 2 2 2 3 x whenλ = 6,let X = x betheeigenvector x then (A - 6 )X = 0 -4 0 4 x 0 0 0 x = 0 4 0 -4 x 0 4x + 4x = 0 4x - 4x = 0 x = x and x isarbitrary x must be so chosen that X and X are orthogonal among th .1 emselves and also each is orthogonal with X
  • 35.
                                  2 3 3 1 3 2 3 1 α Let X = 0 and let X = β 1 γ Since X is orthogonal to X α - γ = 0 ...(4) X is orthogonal to X α + γ = 0 ...(5) Solving (4)and(5), we get α = γ = 0 and β is arbitrary. 0 Taking β = 1, X = 1 0 1 1 0 Modal matrix is M = 0 0 1 -1 1         0
  • 36.
                                                             The normalised modal matrix is 1 1 0 2 2 N = 0 0 1 1 1 - 0 2 2 1 1 0 - 1 1 02 2 2 0 4 2 2 1 1 D = N'AN = 0 0 6 0 0 0 1 2 2 4 0 2 1 1 - 00 1 0 2 2 -2 0 0 D = 0 6 0 which is the required diagonal matrix 0 0 6 .
  • 37.
    Quadratic Forms DEFINITION:- A homogeneouspolynomial of second degree in any number of variables is called a quadratic form. For example, ax2 + 2hxy +by2 ax2 + by2 + cz2 + 2hxy + 2gyz + 2fzx and ax2 + by2 + cz2 + dw2 +2hxy +2gyz + 2fzx + 2lxw + 2myw + 2nzw are quadratic forms in two, three and four variables
  • 38.
    In n –variables x1,x2,…,xn, the general quadratic form is In the expansion, the co-efficient of xixj = (bij + bji). 38    n 1j n 1i jiijjiij bbwhere,xxb ).b(b 2 1 awherexxaxxb baandaawherebb2aSuppose jiijijji n 1j n 1i ijji n 1j n 1i ij iiiijiijijijij      
  • 39.
    Hence every quadraticform can be written as     getweform,matrixin formsquadraticofexamplessaidabovethewritingNow .x,...,x,xXandaAwhere symmetric,alwaysisAmatrixthethatso AX,X'xxa n21ij ji n 1j n 1i ij                 y x bh ha y][xby2hxyax(i) 22
  • 40.
  • 41.
    Two Theorems OnQuadratic Form Theorem(1): A quadratic form can always be expressed with respect to a given coordinate system as where A is a unique symmetric matrix. Theorem2: Two symmetric matrices A and B represent the same quadratic form if and only if B=PTAP where P is a non-singular matrix. AxxY T 
  • 42.
    Nature of QuadraticForm A real quadratic form X’AX in n variables is said to be i. Positive definite if all the eigen values ofA > 0. ii. Negative definite if all the eigen values of A < 0. iii. Positive semi definite if all the eigen values ofA 0 and at least one eigen value = 0. iv. Negative semi definite if all the eigen values of A 0 and at least one eigen value = 0. v. Indefinite if some of the eigen values ofA are + ve and others – ve.
  • 43.
    Find the natureof the following quadratic forms i. x2 + 5y2 + z2 + 2xy + 2yz + 6zx ii. 3x2 + 5y2 + 3z2 – 2yz + 2zx – 2xy Solution:- i. The matrix of the quadratic form is 43 Example :-            113 151 311 A
  • 44.
    The eigen valuesof A are -2, 3, 6. Two of these eigen values being positive and one being negative, the given quadratric form is indefinite. ii. The matrix of the quadratic form is The eigen values of A are 2, 3, 6. All these eigen values being positive, the given quadratic form is positive definite.               311 151 113 A
  • 45.
    Linear Transformation ofa Quadratic Form ▪ Let X’AX be a quadratic form in n- variables and let X = PY ….. (1) where P is a non – singular matrix, be the non – singular transformation. ▪ From (1), X’ = (PY)’ =Y’P’ and hence X’AX =Y’P’APY =Y’(P’AP)Y =Y’BY …. (2) where B = P’AP.
  • 46.
    Therefore,Y’BY is alsoa quadratic form in n- variables. Hence it is a linear transformation of the quadratic form X’AX under the linear transformation X = PY and B = P’AP. Note. (i) Here B = (P’AP)’ = P’AP = B (ii) ρ(B) = ρ(A) Therefore, A and B are congruent matrices.
  • 47.
    Reduce 3x2 +3z2 + 4xy + 8xz + 8yz into canonical form. Or Diagonalises the quadratic form 3x2 + 3z2 + 4xy + 8xz + 8yz by linear transformations and write the linear transformation. Or Reduce the quadratic form 3x2 + 3z2 + 4xy + 8xz + 8yz into the sum of squares. 47 Example:-
  • 48.
    Solution:- The givenquadratic form can be written as X’AX where X = [x, y, z]’ and the symmetric matrix A = Let us reduce A into diagonal matrix. We know tat A = I3AI3.           344 402 423                                          100 010 001 344 402 423 100 010 001 344 402 423
  • 49.
                                               21 31OperatingR ( 2 / 3),R ( 4 / 3) (for A onL.H.S.andpre factor on R.H.S.), we get 3 2 4 1 0 0 1 0 0 4 4 2 0 1 0 A 0 1 0 3 3 3 0 0 1 4 7 4 0 0 1 3 3 3                                                      100 010 3 4 3 2 1 A 10 3 4 01 3 2 001 3 7 3 4 0 3 4 3 4 0 423 getweR.H.S),onfactorpostandL.H.S.onA(for 4/3)(C2/3),(COperating 3121
  • 50.
  • 51.
    The canonical formof the given quadratic form is Here ρ(A) = 3, index = 1, signature = 1 – (2) = -1. Note:- In this problem the non-singular transformation which reduces the given quadratic form into the canonical form is X = PY. i.e.,   2 3 2 2 2 1 3 2 1 321 yy 3 4 3y y y y 100 0 3 4 0 003 yyyAP)Y(P'Y'                                                          3 2 1 112 01 3 2 001 y y y z y x
  • 52.