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CSNB143 – Discrete Structure. MATRIX. MATRIX. Learning Outcomes Students should be able to read matrix and its entries without difficulties. Students should understand all matrices operations. Students should be able to differentiate different matrices and operations by different matrix.

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Matrix
MATRIX

Learning Outcomes

  • Students should be able to read matrix and its entries without difficulties.

  • Students should understand all matrices operations.

  • Students should be able to differentiate different matrices and operations by different matrix.

  • Students should be able to identify Boolean matrices and how to operate them.


Matrix1
MATRIX

Introduction

  • An array of numbers arranged in m horizontal rows and n vertical columns:

  • Ex 1:

    A = a11 a12 ……. a1n

    a21 a22 ……. a2n

    .. .. ..

    .. .. ..

    .. .. ..

    am1 am2 ……. amn

  • The ith row of A is [ai1, ai2, ai3, …ain]; 1 im

  • The jth column of A is a1j

    a2j ; 1 jn

    a3j

    .

    .amj


Matrix2
MATRIX

Diagonal matrix

  • We say that A is a matrix m x n. If m = n, then A is a square matrix of order n, and a11, a22, a33, ..ann form the main diagonal of A.

  • aij which is in the ith row andjth column, is said to be the i,jth element of A or the (i, j) entry of A, often written as A = [aij].

  • A square matrix A = [aij], for which every entry off the main diagonal is zero, that is aij = 0 for i j, is called a diagonal matrix.

  • Ex 2:

    A = 8 0 0 0

    0 3 0 0

    0 0 7 0

    0 0 0 1


Matrix3
MATRIX

  • Two m x n matrices A and B, A = [aij] and B = [bij], are said to be equal if aij = bij for 1 im, 1 jn; that is, if corresponding elements are the same.

  • Ex 3:

    A = a 5 3 B = 1 5 x

    2 7 -1 y 7 -1

    3 b 0 3 4 0

  • So, if A = B, then a = 1, x = 3, y = 2, b = 4.


Matrix4
MATRIX

Matrices Summation

  • If A = [aij] and B = [bij] are m x n matrices, then the sum of A and B is matrix C = [cij], defined by

    cij = aij + bij; 1 im, 1 j n.

  • C is obtained by adding the corresponding elements of A and B.

  • Ex 4:

    A = 1 5 3 B = 2 0 3 C = 3 5 6

    2 7 -1 + 6 1 3 = 8 8 2 3 4 0 -3 1 9 0 5 9

  • The sum of the matrices A and B is defined only when A and B have the same number of rows and the same number of columns (same dimension).


Matrix5
MATRIX

Exercise 1:

a) Identify which matrices that the summation process can be done.

b) Compute C + G, A + D, E + H, A + F.

A = 2 1 B = 2 1 3 C = 7 2 D = 3 3

4 8 4 5 7 4 2 2 5

1 5

E = 2 -3 7 F = -2 -1 G = 4 3 H = 1 2 3

0 4 7 -4 -8 5 1 4 5 6

3 1 2 -1 0 7 8 9


Matrix6
MATRIX

A matrix in when all of its entries are zero is called zero matrix, denoted by 0.

  • Theorems involved in summation :

    • A + B = B + A.

    • (A + B) + C = A + (B + C).

    • A + 0 = 0 + A = A.

      Matrices Product

  • If A = [aij] is an m x p matrix and B = [bij] is a p x n matrix, then the product of A and B, denoted AB, will produce the m x n matrix C = [cij], defined by

    cij = ai1b1j + ai2b2j + … + aipbpj; 1 in, 1 j m

  • That is, elements ai1, ai2, .. aip from ith row of A and elements b1j, b2j, .. bpj from jth column of B, are multiplied for each corresponding entries and add all the products.


Matrix7
MATRIX

Ex 5:

A = 2 3 -4 B = 3 1

1 2 3 -2 2

2 x 3 5 -3

3 x 2

AB = 2(3) + 3(-2) + -4(5) 2(1) + 3(2) + -4(-3)

1(3) + 2(-2) + 3(5) 1(1) + 2(2) + 3(-3)

= 6 – 6 – 20 2 + 6 + 12

3 – 4 + 15 1 + 4 – 9

= -20 20

14 -4 2 x 2

Exercise 2:

a) Identify which matrices that the product process can be done. List all pairs.

b) Compute CA, AD, EG, BE, HE.


Matrix8
MATRIX

  • If A is an m x p matrix and B is a p x n matrix, in which AB will produce m x n, BA might be produce or not depends on:

    • nm, then BA cannot be produced.

    • n = m, pm @ n, then we can get BA but the size will be different from AB.

    • n = m= p, A  B, then we can get BA, the size of BA and AB is the same, but AB  BA.

    • n = m = p, A = B, then we can get BA, the size of BA and AB is the same, and AB = BA.


A B AB B A BA

(m x p) (p x n) (m x n) (p x n) (m x p) ?

2 x 3 3 x 4 2 x 4 3 x 4 2 x 3 X

2 x 3 3 x 2 2 x 2 3 X 2 2 X 3 3 X 3

2 X 2 2 X 2 2 X 2 2 X 2 2 X 2 2 X 2

2 1 3 1 9 5 3 1 2 1 8 6

2 3 3 3 15 11 3 3 2 3 12 12


Matrix9
MATRIX

Identity matrix

  • Let say A is a diagonal matrix n x n. If all entries on its diagonal are 1, it is called identity matrix, ordered n, written as I.

  • Ex 7:

    1 0 1 0 0 1 0 0 0

    0 1 0 1 0 0 1 0 0

    0 0 0 0 0 1 0

    0 0 0 1

  • Theorems involved are:

    • A(BC) = (AB)C.

    • A(B + C) = AB + AC.

    • (A + B)C = AC + BC.

    • IA = AI = A.


Matrix10
MATRIX

Transposition Matrix

  • If A = [aij] is an m x n matrix, then AT = [aij]T is a n x m matrix, where

    aijT= aji; 1 im, 1 jn

  • It is called transposition matrix for A.

  • Ex 8:

    A = 2 -3 5 AT = 2 6

    6 1 3 -3 1

    5 3

  • Theorems involved are:

    • (AT)T = A

    • (A + B)T = AT + BT

    • (AB)T = BTAT


Matrix11
MATRIX

  • Matrix A = [aij] is said to be symmetric if AT = A, that is aij = aji,

  • A is said to be symmetric if all entries are symmetrical to its main diagonal.

  • Ex 9:

    A = 12 -3 B = 1 2 -3

    245 2 4 0

    -356 3 2 1

    Symmetric Not Symmetric, why?


Matrix12
MATRIX

Boolean Matrix and Its Operations

  • Boolean matrix is an m x n matrix where all of its entries are either 1 or 0 only.

  • There are three operations on Boolean:

  • Join by

    Given A = [aij] and B = [bij] are Boolean matrices with the same dimension, join by A and B, written as A  B, will produce a matrix C = [cij], where

    cij = 1 if aij = 1 OR bij = 1

    0 if aij = 0 AND bij = 0

  • Meet

    Meetfor A and B, both with the same dimension, written as A  B, will produce matrix D = [dij] where

    dij= 1 if aij = 1 AND bij = 1

    0 if aij = 0 OR bij = 0


Matrix13
MATRIX

  • Ex 10: A = 1 0 1 B = 1 1 0

  • 0 1 1 0 0 1

  • 1 1 0 0 1 0

  • 0 1 0 1 1 0

  • A  B = 1 1 1 A  B = 1 0 0

  • 0 1 1 0 0 1

  • 1 1 0 0 1 0

  • 1 1 0 0 1 0


Matrix14
MATRIX

  • Boolean product

  • If A = [aij] is an m x p Boolean matrix, and B = [bij] is a p x n Boolean matrix, we can get a Boolean product for A and B written as A ⊙ B, producing C, where:

  • cij = 1 if aik = 1 AND bkj = 1; 1 kp.

    0 other than that

  • It is using the same way as normal matrix product.


Matrix15
MATRIX

  • Ex 11:

  • A = 1 0 0 0 B = 1 1 0

  • 0 1 1 0 0 1 0

  • 1 0 1 1 1 1 0

  • 3 x 4 0 0 1

    4 x 3

    A ⊙ B = 1 + 0 + 0 + 0 1 + 0 + 0 + 0 0 + 0 + 0 + 0

    0 + 0 + 1 + 0 0 + 1 + 1 + 0 0 + 0 + 0 + 0

    1 + 0 + 1 + 0 1 + 0 + 1 + 0 0 + 0 + 0 + 1

  • A ⊙ B = 1 1 0

    1 1 0

    1 1 1

    3 x 3


Matrix16
MATRIX

  • Exercise 3:

  • A = 1 0 0 0 B = 0 1 0 0 C = 0 0 1 0

    0 1 1 0 0 0 1 1 1 0 0 0

    0 0 0 1 0 1 0 1 1 1 0 0

    1 1 0 0 0 0 1 0 1 1 1 0

  • Find:

    • A  B

    • A  B

    • A ⊙ B

    • A  C

    • A C

    • A ⊙ C

    • B  C

    • B  C

    • B ⊙ C


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