![Matrices - Introduction
A matrix is denoted by a bold capital letter and the elements within the matrix
are denoted by lower case letters
e.g. matrix [A] with elements aij
mnijmm
nij
inij
aaaa
aaaa
aaaa
21
22221
1211
...
...
i goes from 1 to m
j goes from 1 to n
Amxn=
mAn](https://image.slidesharecdn.com/r-181005115505/85/R-Ganesh-Kumar-30-320.jpg)
R.Ganesh Kumar
- 27. MATRICES
- 28. Matrices - Introduction Matrix algebra has at least two advantages: •Reduces complicated systems of equations to simple expressions •Adaptable to systematic method of mathematical treatment and well suited to computers Definition: A matrix is a set or group of numbers arranged in a square or rectangular array enclosed by two brackets 11 03 24 dc ba
- 29. Matrices - Introduction Properties: •A specified number of rows and a specified number of columns •Two numbers (rows x columns) describe the dimensions or size of the matrix. Examples: 3x3 matrix 2x4 matrix 1x2 matrix 333 514 421 2 3 3 3 0 1 0 1 11
- 30. Matrices - Introduction A matrix is denoted by a bold capital letter and the elements within the matrix are denoted by lower case letters e.g. matrix [A] with elements aij mnijmm nij inij aaaa aaaa aaaa 21 22221 1211 ... ... i goes from 1 to m j goes from 1 to n Amxn= mAn
- 31. Matrices - Introduction TYPES OF MATRICES 1. Column matrix or vector: The number of rows may be any integer but the number of columns is always 1 2 4 1 3 1 1 21 11 ma a a 2. Row matrix or vector Any number of columns but only one row 611 2530 naaaa 1131211
- 32. 3. Rectangular matrix Contains more than one element and number of rows is not equal to the number of columns 67 77 73 11 03302 00111 nm 4. Square matrix The number of rows is equal to the number of columns (a square matrix A has an order of m) m x m 03 11 166 099 111 The principal or main diagonal of a square matrix is composed of all elements aij for which i=j
- 33. 5. Diagonal matrix A square matrix where all the elements are zero except those on the main diagonal 100 020 001 9000 0500 0030 0003 i.e. aij =0 for all i = j aij = 0 for some or all i = j 6. Unit or Identity matrix - I A diagonal matrix with ones on the main diagonal 1000 0100 0010 0001 10 01 ij ij a a 0 0 i.e. aij =0 for all i = j aij = 1 for some or all i = j
- 34. 7. Null (zero) matrix - 0 All elements in the matrix are zero 0 0 0 000 000 000 0ija 8. Triangular matrix A square matrix whose elements above or below the main diagonal are all zero 325 012 001 325 012 001 300 610 981
- 35. 8a. Upper triangular matrix A square matrix whose elements below the main diagonal are all zero i.e. aij = 0 for all i > j 300 810 781 3000 8700 4710 4471 ij ijij ijijij a aa aaa 00 0 8b. Lower triangular matrix A square matrix whose elements above the main diagonal are all zero ijijij ijij ij aaa aa a 0 00 325 012 001 i.e. aij = 0 for all i < j
- 36. 9. Scalar matrix A diagonal matrix whose main diagonal elements are equal to the same scalar A scalar is defined as a single number or constant 100 010 001 6000 0600 0060 0006 i.e. aij = 0 for all i = j aij = a for all i = j ij ij ij a a a 00 00 00
- 38. Matrices - Operations EQUALITY OF MATRICES Two matrices are said to be equal only when all corresponding elements are equal Therefore their size or dimensions are equal as well 325 012 001 325 012 001 A = B = A = B Some properties of equality: •IIf A = B, then B = A for all A and B •IIf A = B, and B = C, then A = C for all A, B and C 325 012 001 333231 232221 131211 bbb bbb bbb A = B = If A = B then ijij ba
- 39. Matrices - OperationsADDITION AND SUBTRACTION OF MATRICES The sum or difference of two matrices, A and B of the same size yields a matrix C of the same size ijijij bac Matrices of different sizes cannot be added or subtracted Commutative Law: A + B = B + A Associative Law: A + (B + C) = (A + B) + C = A + B + C 972 588 324 651 652 137 A 2x3 B 2x3 C 2x3
- 40. Matrices - Operations 2221 1211 3231 2221 1211 232221 131211 cc cc bb bb bb aaa aaa 22322322221221 21312321221121 12321322121211 11311321121111 )()()( )()()( )()()( )()()( cbababa cbababa cbababa cbababa Successive multiplication of row i of A with column j of B – row by column multiplication
- 41. Matrices - Operations )37()22()84()57()62()44( )33()22()81()53()62()41( 35 26 84 724 321 5763 2131 Remember also: IA = A 10 01 5763 2131 5763 2131
- 42. Matrices - Operations Assuming that matrices A, B and C are conformable for the operations indicated, the following are true: 1. AI = IA = A 2. A(BC) = (AB)C = ABC - (associative law) 3. A(B+C) = AB + AC - (first distributive law) 4. (A+B)C = AC + BC - (second distributive law) Caution! 1. AB not generally equal to BA, BA may not be conformable 2. If AB = 0, neither A nor B necessarily = 0 3. If AB = AC, B not necessarily = C
- 43. Matrices - Operations AB not generally equal to BA, BA may not be conformable 010 623 05 21 20 43 2015 83 20 43 05 21 20 43 05 21 ST TS S T If AB = 0, neither A nor B necessarily = 0 00 00 32 32 00 11
- 44. Matrices - Operations TRANSPOSE OF A MATRIX If : 135 7423 2 AA 2x3 17 34 52 3 2 TT AA Then transpose of A, denoted AT is: T jiij aa For all i and j
- 45. Matrices - OperationsTo transpose: Interchange rows and columns The dimensions of AT are the reverse of the dimensions of A 135 7423 2 AA 17 34 52 2 3 TT AA 2 x 3 3 x 2
- 46. Matrices - OperationsProperties of transposed matrices: 1. (A+B)T = AT + BT 2. (AB)T = BT AT 3. (kA)T = kAT 4. (AT)T = A 1. (A+B)T = AT + BT 972 588 324 651 652 137 95 78 28 95 78 28 36 25 41 61 53 27
- 47. Matrices - Operations (AB)T = BT AT 82 30 21 01 211 82 8 2 2 1 1 320 011
- 48. Matrices - Operations SYMMETRIC MATRICES A Square matrix is symmetric if it is equal to its transpose: A = AT db ba A db ba A T
- 49. Matrices - Operations When the original matrix is square, transposition does not affect the elements of the main diagonal db ca A dc ba A T The identity matrix, I, a diagonal matrix D, and a scalar matrix, K, are equal to their transpose since the diagonal is unaffected.
- 50. Matrices - Operations INVERSE OF A MATRIX Consider a scalar k. The inverse is the reciprocal or division of 1 by the scalar. Example: k=7 the inverse of k or k-1 = 1/k = 1/7 Division of matrices is not defined since there may be AB = AC while B = C Instead matrix inversion is used. The inverse of a square matrix, A, if it exists, is the unique matrix A-1 where: AA-1 = A-1 A = I
- 52. Matrices - Operations ADJOINT MATRICES A cofactor matrix C of a matrix A is the square matrix of the same order as A in which each element aij is replaced by its cofactor cij . Example: 43 21 A 12 34 C If The cofactor C of A is
- 53. Matrices - Operations The adjoint matrix of A, denoted by adj A, is the transpose of its cofactor matrix T CadjA It can be shown that: A(adj A) = (adjA) A = |A| I Example: 13 24 10)3)(2()4)(1( 43 21 T CadjA A A IadjAA 10 100 010 13 24 43 21 )( IAadjA 10 100 010 43 21 13 24 )(
- 54. Matrices - OperationsUSING THE ADJOINT MATRIX IN MATRIX INVERSION A adjA A 1 Since AA-1 = A-1 A = I and A(adj A) = (adjA) A = |A| I then Example 43 21 A = 1.03.0 2.04.0 13 24 10 11 A AA-1 = A-1 A = I IAA IAA 10 01 43 21 1.03.0 2.04.0 10 01 1.03.0 2.04.0 43 21 1 1 To check
- 55. Simple 2 x 2 case So that for a 2 x 2 matrix the inverse can be constructed in a simple fashion as ac bd A A a A c A b A d 1 •Exchange elements of main diagonal •Change sign in elements off main diagonal •Divide resulting matrix by the determinant zy xw A 1
- 56. Simple 2 x 2 case Example 2.04.0 3.01.0 24 31 10 1 14 32 1 A A Check inverse A-1 A=I I 10 01 14 32 24 31 10 1
- 57. Linear Equations
- 58. Linear EquationsLinear equations are common and important for survey problems Matrices can be used to express these linear equations and aid in the computation of unknown values Example n equations in n unknowns, the aij are numerical coefficients, the bi are constants and the xj are unknowns nnnnnn nn nn bxaxaxa bxaxaxa bxaxaxa 2211 22222121 11212111
- 59. Linear Equations The equations may be expressed in the form AX = B where ,, 2 1 11 22221 11211 nnnnn n n x x x X aaa aaa aaa A and nb b b B 2 1 n x n n x 1 n x 1 Number of unknowns = number of equations = n
- 60. Linear Equations If the determinant is nonzero, the equation can be solved to produce n numerical values for x that satisfy all the simultaneous equations To solve, premultiply both sides of the equation by A-1 which exists because |A| = 0 A-1 AX = A-1 B Now since A-1 A = I We get X = A-1 B So if the inverse of the coefficient matrix is found, the unknowns, X would be determined
- 61. Linear Equations Example 32 12 23 321 21 321 xxx xx xxx The equations can be expressed as 3 1 2 121 012 113 3 2 1 x x x