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Structure of this lecture
• Basic info on myself and this module
• Essential of matrix arithmetic
• Multiple regression models
• Statistical inference and hypothesis testing
Main learning outcomes:
- Basic understanding of matrix algebra
- Basic understanding of classical linear regression model assumptions
- Basic understanding of how to construct and interpret a hypothesis test
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Dr Enrico Onali
Division: Financial Studies
Location: Room 2.07, Alun Building
Telephone: 01248 38 3650
Email: [email protected]
Office hours:
Monday 11.30-12.30
Monday 13.30-14.30
or by appointment
My contact details
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Who am I?
• Senior Lecturer in Finance
• Italian
• Experience in Italian retail bank
• Current research interests: Banking and financial regulation, dividend policy, market efficiency, applied econometrics
• Profile at Google Scholar:http://scholar.google.co.uk/citations?user=cro4BU0AAAAJ&hl=it&oi=ao
Links to my publications (access from BU intranet needed):http://www.sciencedirect.com/science/article/pii/S0278425414000696
http://onlinelibrary.wiley.com/doi/10.1111/jbfa.12057/abstract
http://0-www.sciencedirect.com.unicat.bangor.ac.uk/science/article/pii/S1057521912000579
http://0-www.sciencedirect.com.unicat.bangor.ac.uk/science/article/pii/S0165176512002844
http://0-www.sciencedirect.com.unicat.bangor.ac.uk/science/article/pii/S1057521911000123
http://0-www.sciencedirect.com.unicat.bangor.ac.uk/science/article/pii/S1057521909000337
http://0-onlinelibrary.wiley.com.unicat.bangor.ac.uk/doi/10.1111/j.1467-646X.2010.01037.x/full3
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Financial econometrics What is it? Why is it useful?
• Financial econometrics: Basically, a branch of applied mathematics
• Dissertation: This module will be very helpful for those of you who decide to write a dissertation
• Employability: employers like people with numeracy skills, although returns to skills vary with the country
http://www.economist.com/blogs/freeexchange/2014/01/economic-value-skills
Those of you who plan to work in the academia, central banks, think-tanks, will find this module extremely useful.
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Short course overview
• Technical background (today)
• Regression analysis using time series data
• Univariate modelling of stationary time series variables
• Modelling non-stationary time series variables
• Multivariate modelling of stationary time series variables
• Cointegration and multivariate modelling of non-stationary time series
• Modelling volatility in financial time series data
• Panel data econometrics
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Textbook and readings
Main textbook:
C. Brooks. Introductory econometrics for finance, 2nd edition. Cambridge University Press, 2008.
C. Brooks. Introductory econometrics for finance, 3rd edition. Cambridge University Press, 2014.
Other references:
B.H. Baltagi. Econometric analysis of panel data, 4th ed., Wiley 2008.
W. Enders. Applied econometric time series, 2nd ed., Wiley, 2005.
W.H. Greene. Econometric analysis, 6th edition, Prentice Hall, 2002.
G. Koop. Analysis of financial data, Wiley, 2006.
M. Verbeek. A guide to modern econometrics, 3rd ed., Wiley, 2008.
C. Cameron and P. K. Trivedi. Microeconometrics Using Stata, Revised Edition. Stata Press, 2010.
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1. TECHNICAL BACKGROUND
Essentials of matrix arithmetic
(Several of the examples used here are taken from Brooks pp.611-615,
2nd edition or pp. 41-48, 3rd edition).
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1. TECHNICAL BACKGROUND
Essentials of matrix arithmetic
(Several of the examples used here are taken from Brooks pp.611-615,
2nd edition or pp. 41-48, 3rd edition).
Notation and special types of matrix
A matrix is a collection or array of numbers. In econometrics, it is often
convenient to use matrices to represent data. Using matrices, we can write
down concise formulae for estimators or test statistics in terms of the data
from which they are computed.
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1. TECHNICAL BACKGROUND
Essentials of matrix arithmetic
(Several of the examples used here are taken from Brooks pp.611-615,
2nd edition or pp. 41-48, 3rd edition).
Notation and special types of matrix
A matrix is a collection or array of numbers. In econometrics, it is often
convenient to use matrices to represent data. Using matrices, we can write
down concise formulae for estimators or test statistics in terms of the data
from which they are computed.
The dimensions of a matrix are quoted as (RC), where R = number of
rows, C = number of columns.
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1. TECHNICAL BACKGROUND
Essentials of matrix arithmetic
(Several of the examples used here are taken from Brooks pp.611-615,
2nd edition or pp. 41-48, 3rd edition).
Notation and special types of matrix
A matrix is a collection or array of numbers. In econometrics, it is often
convenient to use matrices to represent data. Using matrices, we can write
down concise formulae for estimators or test statistics in terms of the data
from which they are computed.
The dimensions of a matrix are quoted as (RC), where R = number of
rows, C = number of columns.
Each element of a matrix is referred to using subscripts. For the matrix A,
ai,j refers to the element in the i’th row and the j’th column of A. If the
dimensions of A are (23), we can write:
A =
3,22,21,2
3,12,11,1
aaa
aaa
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Essentials of matrix arithmetic (cont'd)
A matrix with only one row, or dimensions of (1C), is known as a row
vector.
A matrix with only one column, or dimensions of (R1), is known as a
column vector.
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Essentials of matrix arithmetic (cont'd)
A matrix with only one row, or dimensions of (1C), is known as a row
vector.
A matrix with only one column, or dimensions of (R1), is known as a
column vector.
A square matrix has the same number of rows and columns.
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Essentials of matrix arithmetic (cont'd)
A matrix with only one row, or dimensions of (1C), is known as a row
vector.
A matrix with only one column, or dimensions of (R1), is known as a
column vector.
A square matrix has the same number of rows and columns.
A diagonal matrix is a square matrix with non-zero values on the main
diagonal, and 0’s in all other elements. For example:
A =
1000
0200
0010
0003
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Essentials of matrix arithmetic (cont'd)
An identity matrix, denoted I or Im (where m denotes the number of rows
and columns), is a square matrix with 1’s in all elements on the main
diagonal, and 0’s in all other elements.
I2 =
10
01
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Essentials of matrix arithmetic (cont'd)
An identity matrix, denoted I or Im (where m denotes the number of rows
and columns), is a square matrix with 1’s in all elements on the main
diagonal, and 0’s in all other elements.
I2 = I3 =
10
01
100
010
001
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Essentials of matrix arithmetic (cont'd)
An identity matrix, denoted I or Im (where m denotes the number of rows
and columns), is a square matrix with 1’s in all elements on the main
diagonal, and 0’s in all other elements.
I2 = I3 = I4 =
10
01
100
010
001
1000
0100
0010
0001
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Essentials of matrix arithmetic (cont'd)
An identity matrix, denoted I or Im (where m denotes the number of rows
and columns), is a square matrix with 1’s in all elements on the main
diagonal, and 0’s in all other elements.
I2 = I3 = I4 =
A symmetric matrix is a square matrix that is symmetric around the main
diagonal, so that ai,j=aj,i for all i and j. For example:
A =
10
01
100
010
001
1000
0100
0010
0001
0897
8264
9632
7421
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Essentials of matrix arithmetic (cont'd)
Addition and subtraction
Two matrices can be added or subtracted if (and only if) both matrices
have the same dimensions. If so, the corresponding elements of the two
matrices are added or subtracted one by one.
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Essentials of matrix arithmetic (cont'd)
Addition and subtraction
Two matrices can be added or subtracted if (and only if) both matrices
have the same dimensions. If so, the corresponding elements of the two
matrices are added or subtracted one by one.
If A = and B =
7.01.0
6.03.0
3.00
1.02.0
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Essentials of matrix arithmetic (cont'd)
Addition and subtraction
Two matrices can be added or subtracted if (and only if) both matrices
have the same dimensions. If so, the corresponding elements of the two
matrices are added or subtracted one by one.
If A = and B =
A + B = =
7.01.0
6.03.0
3.00
1.02.0
3.07.001.0
1.06.02.03.0
11.0
5.05.0
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Essentials of matrix arithmetic (cont'd)
Addition and subtraction
Two matrices can be added or subtracted if (and only if) both matrices
have the same dimensions. If so, the corresponding elements of the two
matrices are added or subtracted one by one.
If A = and B =
A + B = =
A – B = =
7.01.0
6.03.0
3.00
1.02.0
3.07.001.0
1.06.02.03.0
11.0
5.05.0
3.07.001.0
1.06.02.03.0
4.01.0
7.01.021
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Essentials of matrix arithmetic (cont'd)
Multiplication
(i) Scalar multiplication
To multiply a matrix by a scalar (a single number), every element of the
matrix is multiplied by that number.
If A = then 2A = 2 =
7.01.0
6.03.0
7.01.0
6.03.0
4.12.0
2.16.0
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Essentials of matrix arithmetic (cont'd)
Multiplication
(i) Scalar multiplication
To multiply a matrix by a scalar (a single number), every element of the
matrix is multiplied by that number.
If A = then 2A = 2 =
(ii) Matrix multiplication
Two matrices can be multiplied together if (and only if) the number of
columns in the 1st matrix equals the number of rows in the 2nd matrix.
The number of rows in the 1st matrix determines the number of rows in
the product matrix, and the number of columns in the 2nd matrix
determines the number of columns in the product matrix.
7.01.0
6.03.0
7.01.0
6.03.0
4.12.0
2.16.0
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Essentials of matrix arithmetic (cont'd)
Multiplication (cont'd)
In other words, A and B can be multiplied together if A is (mn) and B is
(np). The dimensions of C=AB are (mp).
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Essentials of matrix arithmetic (cont'd)
Multiplication (cont'd)
In other words, A and B can be multiplied together if A is (mn) and B is
(np). The dimensions of C=AB are (mp).
The element in the i’th row and j’th column of the product matrix is
obtained by summing the products of the corresponding elements in the
i’th row of the 1st matrix and the j’th column of the 2nd matrix.
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Essentials of matrix arithmetic (cont'd)
Multiplication (cont'd)
In other words, A and B can be multiplied together if A is (mn) and B is
(np). The dimensions of C=AB are (mp).
The element in the i’th row and j’th column of the product matrix is
obtained by summing the products of the corresponding elements in the
i’th row of the 1st matrix and the j’th column of the 2nd matrix.
Let A = and B =
61
37
21
2036
9420
26
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Essentials of matrix arithmetic (cont'd)
Multiplication (cont'd)
In other words, A and B can be multiplied together if A is (mn) and B is
(np). The dimensions of C=AB are (mp).
The element in the i’th row and j’th column of the product matrix is
obtained by summing the products of the corresponding elements in the
i’th row of the 1st matrix and the j’th column of the 2nd matrix.
Let A = and B =
The dimensions of A are (32) and the dimensions of B are (24).
Therefore the dimensions of C=AB are (34).
Let C =
61
37
21
2036
9420
4,33,32,31,3
4,23,22,21,2
4,13,12,11,1
cccc
cccc
cccc
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Essentials of matrix arithmetic (cont'd)
Multiplication (cont'd) A = B =
c1,1 is the sum of the products of the 1st row of A and the 1st column of B
c1,1 = 10 + 26 = 12
61
37
21
2036
9420
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Essentials of matrix arithmetic (cont'd)
Multiplication (cont'd) A = B =
c1,1 is the sum of the products of the 1st row of A and the 1st column of B
c1,1 = 10 + 26 = 12
c1,2 is the sum of the products of the 1st row of A and the 2nd column of B
c1,2 = 12 + 23 = 8
61
37
21
2036
9420
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Essentials of matrix arithmetic (cont'd)
Multiplication (cont'd) A = B =
c1,1 is the sum of the products of the 1st row of A and the 1st column of B
c1,1 = 10 + 26 = 12
c1,2 is the sum of the products of the 1st row of A and the 2nd column of B
c1,2 = 12 + 23 = 8
c1,3 is the sum of the products of the 1st row of A and the 3rd column of B
c1,3 = 14 + 20 = 4
61
37
21
2036
9420
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Essentials of matrix arithmetic (cont'd)
Multiplication (cont'd) A = B =
c1,1 is the sum of the products of the 1st row of A and the 1st column of B:
c1,1 = 10 + 26 = 12
c1,2 is the sum of the products of the 1st row of A and the 2nd column of B:
c1,2 = 12 + 23 = 8
c1,3 is the sum of the products of the 1st row of A and the 3rd column of B:
c1,3 = 14 + 20 = 4
c1,4 is the sum of the products of the 1st row of A and the 4th column of B
c1,4 = 19 + 22 = 13
61
37
21
2036
9420
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Essentials of matrix arithmetic (cont'd)
Multiplication (cont'd) A = B =
c1,1 is the sum of the products of the 1st row of A and the 1st column of B:
c1,1 = 10 + 26 = 12
c1,2 is the sum of the products of the 1st row of A and the 2nd column of B:
c1,2 = 12 + 23 = 8
c1,3 is the sum of the products of the 1st row of A and the 3rd column of B:
c1,3 = 14 + 20 = 4
c1,4 is the sum of the products of the 1st row of A and the 4th column of B:
c1,4 = 19 + 22 = 13
c2,1 is the sum of the products of the 2nd row of A and the 1st column of B
c2,1 = 70 + 36 = 18
61
37
21
2036
9420
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Essentials of matrix arithmetic (cont'd)
Multiplication (cont'd) A = B =
c1,1 is the sum of the products of the 1st row of A and the 1st column of B:
c1,1 = 10 + 26 = 12
c1,2 is the sum of the products of the 1st row of A and the 2nd column of B:
c1,2 = 12 + 23 = 8
c1,3 is the sum of the products of the 1st row of A and the 3rd column of B:
c1,3 = 14 + 20 = 4
c1,4 is the sum of the products of the 1st row of A and the 4th column of B:
c1,4 = 19 + 22 = 13
c2,1 is the sum of the products of the 2nd row of A and the 1st column of B:
c2,1 = 70 + 36 = 18
c2,2 is the sum of the products of the 2nd row of A and the 2nd column of B
c2,2 = 72 + 33 = 23
and so on.
61
37
21
2036
9420
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Essentials of matrix arithmetic (cont'd)
Multiplication (cont'd)
The full product matrix C is as follows:
C = AB = =
61
37
21
2036
9420
2142036
69282318
134812
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Essentials of matrix arithmetic (cont'd)
Multiplication (cont'd)
The full product matrix C is as follows:
C = AB = =
Note that in this case the product matrix AB exists, but the product matrix
BA does not exist, because the number of columns in B the number of
rows in A.
61
37
21
2036
9420
2142036
69282318
134812
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Essentials of matrix arithmetic (cont'd)
Multiplication (cont'd)
The full product matrix C is as follows:
C = AB = =
Note that in this case the product matrix AB exists, but the product matrix
BA does not exist, because the number of columns in B the number of
rows in A.
Transposition
The transpose of an (RC) matrix A, written A', is the (CR) matrix
obtained by transposing (switching) the rows and columns of the matrix
A.
61
37
21
2036
9420
2142036
69282318
134812
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Essentials of matrix arithmetic (cont'd)
Multiplication (cont'd)
The full product matrix C is as follows:
C = AB = =
Note that in this case the product matrix AB exists, but the product matrix
BA does not exist, because the number of columns in B the number of
rows in A.
Transposition
The transpose of an (RC) matrix A, written A', is the (CR) matrix
obtained by transposing (switching) the rows and columns of the matrix
A.
If A = A' =
61
37
21
2036
9420
2142036
69282318
134812
61
37
21
632
17137
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Essentials of matrix arithmetic (cont'd)
Rank
The rank of any matrix is the number of linearly independent rows or
columns. Loosely speaking, two rows are linearly independent if it is not
possible to express one of the rows as a multiple of another.
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Essentials of matrix arithmetic (cont'd)
Rank (cont'd)
Suppose A = and B = and C =
rank(A) = 2, because row 2 cannot be expressed as a multiple of row 1 (or
vice versa). Therefore A has two linearly independent rows.
21
34
42
63
00
00
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Essentials of matrix arithmetic (cont'd)
Rank (cont'd)
Suppose A = and B = and C =
rank(A) = 2, because row 2 cannot be expressed as a multiple of row 1 (or
vice versa). Therefore A has two linearly independent rows.
rank(B) = 1, because row 1 is 1.5 times row 2. Therefore rows 1 and 2 are
not linearly independent: B has only one linearly independent row.
21
34
42
63
00
00
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Essentials of matrix arithmetic (cont'd)
Rank (cont'd)
Suppose A = and B = and C =
rank(A) = 2, because row 2 cannot be expressed as a multiple of row 1 (or
vice versa). Therefore A has two linearly independent rows.
rank(B) = 1, because row 1 is 1.5 times row 2. Therefore rows 1 and 2 are
not linearly independent: B has only one linearly independent row.
rank(C) = 0, because a square matrix containing zeros only has no
independent rows.
21
34
42
63
00
00
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Essentials of matrix arithmetic (cont'd)
Rank (cont'd)
Suppose A = and B = and C =
rank(A) = 2, because row 2 cannot be expressed as a multiple of row 1 (or
vice versa). Therefore A has two linearly independent rows.
rank(B) = 1, because row 1 is 1.5 times row 2. Therefore rows 1 and 2 are
not linearly independent: B has only one linearly independent row.
rank(C) = 0, because a square matrix containing zeros only has no
independent rows.
A square matrix A with dimensions (mm) is said to have full rank if
rank(A) = m.
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Essentials of matrix arithmetic (cont'd)
Matrix inversion
For any square matrix that has full rank, an inverse matrix can be defined
such that the product of the original matrix and the inverse matrix is an
identity matrix. In this case, the order in which the two matrices are
multiplied does not matter.
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Essentials of matrix arithmetic (cont'd)
Matrix inversion
For any square matrix that has full rank, an inverse matrix can be defined
such that the product of the original matrix and the inverse matrix is an
identity matrix. In this case, the order in which the two matrices are
multiplied does not matter.
If the original matrix is A, the inverse matrix is denoted A–1.
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Essentials of matrix arithmetic (cont'd)
Matrix inversion
For any square matrix that has full rank, an inverse matrix can be defined
such that the product of the original matrix and the inverse matrix is an
identity matrix. In this case, the order in which the two matrices are
multiplied does not matter.
If the original matrix is A, the inverse matrix is denoted A–1.
If A is (mm), AA–1 = A–1A = Im
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Essentials of matrix arithmetic (cont'd)
Matrix inversion
For any square matrix that has full rank, an inverse matrix can be defined
such that the product of the original matrix and the inverse matrix is an
identity matrix. In this case, the order in which the two matrices are
multiplied does not matter.
If the original matrix is A, the inverse matrix is denoted A–1.
If A is (mm), AA–1 = A–1A = Im
If A is (22), the formula for A–1 is relatively simple.
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Essentials of matrix arithmetic (cont'd)
Matrix inversion
For any square matrix that has full rank, an inverse matrix can be defined
such that the product of the original matrix and the inverse matrix is an
identity matrix. In this case, the order in which the two matrices are
multiplied does not matter.
If the original matrix is A, the inverse matrix is denoted A–1.
If A is (mm), AA–1 = A–1A = Im
If A is (22), the formula for A–1 is relatively simple.
If A = then A–1 =
dc
ba
ac
bd
bcad
1
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Essentials of matrix arithmetic (cont'd)
Matrix inversion (cont'd)
Suppose A =
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Essentials of matrix arithmetic (cont'd)
Matrix inversion (cont'd)
Suppose A = A–1 =
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1324
1
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Essentials of matrix arithmetic (cont'd)
Matrix inversion (cont'd)
Suppose A = A–1 =
= =
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32
1324
1
41
32
5
1
8.02.0
6.04.0
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Essentials of matrix arithmetic (cont'd)
Matrix inversion (cont'd)
Suppose A = A–1 =
= =
Check: AA–1 = = = I2
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34
41
32
1324
1
41
32
5
1
8.02.0
6.04.0
21
34
8.02.0
6.04.0
10
01
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Essentials of matrix arithmetic (cont'd)
Matrix inversion (cont'd)
Suppose A = A–1 =
= =
Check: AA–1 = = = I2
If A is (22) as above, the quantity (ad – bc) is known as the determinant
of matrix A, also denoted det(A) or |A|.
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34
41
32
1324
1
41
32
5
1
8.02.0
6.04.0
21
34
8.02.0
6.04.0
10
01
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Essentials of matrix arithmetic (cont'd)
Matrix inversion (cont'd)
The determinant can be interpreted as a summary measure of the
‘information’ contained in the matrix, in the form of a single numerical
value.
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Essentials of matrix arithmetic (cont'd)
Matrix inversion (cont'd)
The determinant can be interpreted as a summary measure of the
‘information’ contained in the matrix, in the form of a single numerical
value.
If A is (mm) where m>2, the formulae for det(A) and A–1 is more
complex. det(A) and A–1 would not usually be calculated manually.
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Essentials of matrix arithmetic (cont'd)
Matrix inversion (cont'd)
The determinant can be interpreted as a summary measure of the
‘information’ contained in the matrix, in the form of a single numerical
value.
If A is (mm) where m>2, the formulae for det(A) and A–1 is more
complex. det(A) and A–1 would not usually be calculated manually.
The inverse of an (mm) matrix A only exists if rank(A)=m.
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Essentials of matrix arithmetic (cont'd)
Matrix inversion (cont'd)
The determinant can be interpreted as a summary measure of the
‘information’ contained in the matrix, in the form of a single numerical
value.
If A is (mm) where m>2, the formulae for det(A) and A–1 is more
complex. det(A) and A–1 would not usually be calculated manually.
The inverse of an (mm) matrix A only exists if rank(A)=m.
Trace and eigenvalues of a square matrix
Two other useful summary measures of the ‘information’ contained in a
square matrix are the trace and the eigenvalues. The trace of any square
matrix is the sum of the main-diagonal elements (from top-left to bottom-
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Essentials of matrix arithmetic (cont'd)
Trace and eigenvalues of a square matrix (cont'd)
The eigenvalues of an (mm) square matrix A are the m solutions
(1,2, ... ,m) to the m’th order polynomial in that is formed by the
expression det(A–Im)=0 or |A–Im|=0, listed in descending order of
absolute magnitude.
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Essentials of matrix arithmetic (cont'd)
Trace and eigenvalues of a square matrix (cont'd)
The eigenvalues of an (mm) square matrix A are the m solutions
(1,2, ... ,m) to the m’th order polynomial in that is formed by the
expression det(A–Im)=0 or |A–Im|=0, listed in descending order of
absolute magnitude.
For A =
A – Im = – = – =
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01
21
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0
0
21
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Essentials of matrix arithmetic (cont'd)
Trace and eigenvalues of a square matrix (cont'd)
The eigenvalues of an (mm) square matrix A are the m solutions
(1,2, ... ,m) to the m’th order polynomial in that is formed by the
expression det(A–Im)=0 or |A–Im|=0, listed in descending order of
absolute magnitude.
For A =
A – Im = – = – =
det(A – Im) = (4 – )(2 – ) – 3 1 = 8 – 6 + 2 – 3 = 2 – 6 + 5
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34
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01
21
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0
0
21
34
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Essentials of matrix arithmetic (cont'd)
Trace and eigenvalues of a square matrix (cont'd)
The eigenvalues of an (mm) square matrix A are the m solutions
(1,2, ... ,m) to the m’th order polynomial in that is formed by the
expression det(A–Im)=0 or |A–Im|=0, listed in descending order of
absolute magnitude.
For A =
A – Im = – = – =
det(A – Im) = (4 – )(2 – ) – 3 1 = 8 – 6 + 2 – 3 = 2 – 6 + 5
det(A – Im) = 0 2 – 6 + 5 = 0
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21
34
10
01
21
34
0
0
21
34
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Essentials of matrix arithmetic (cont'd)
Trace and eigenvalues of a square matrix (cont'd)
The eigenvalues of an (mm) square matrix A are the m solutions
(1,2, ... ,m) to the m’th order polynomial in that is formed by the
expression det(A–Im)=0 or |A–Im|=0, listed in descending order of
absolute magnitude.
For A =
A – Im = – = – =
det(A – Im) = (4 – )(2 – ) – 3 1 = 8 – 6 + 2 – 3 = 2 – 6 + 5
det(A – Im) = 0 2 – 6 + 5 = 0
( – 5)( – 1) = 0
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21
34
10
01
21
34
0
0
21
34
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Essentials of matrix arithmetic (cont'd)
Trace and eigenvalues of a square matrix (cont'd)
The eigenvalues of an (mm) square matrix A are the m solutions
(1,2, ... ,m) to the m’th order polynomial in that is formed by the
expression det(A–Im)=0 or |A–Im|=0, listed in descending order of
absolute magnitude.
For A =
A – Im = – = – =
det(A – Im) = (4 – )(2 – ) – 3 1 = 8 – 6 + 2 – 3 = 2 – 6 + 5
det(A – Im) = 0 2 – 6 + 5 = 0
( – 5)( – 1) = 0
1 = 5 and 2 = 1 are the eigenvalues of the matrix A.
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Essentials of matrix arithmetic (cont'd)
Why are eigenvalues useful?
There are important properties of eigenvalues, in particular:
1. The sum of the eigenvalues is the trace of the matrix
2. The product of the eigenvalues is the determinant
3. The number of non-zero eigenvalues is the rank
Thus, eigenvalues are important to understand whether a matrix
is of full rank, and whether all rows are linearly independent
(this is important, in particular, for the concept of co-
integration)