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Overview
• Definitions• Basic matrix operations (+, -, x)• Determinants and inverses
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Some Definitions …
• Zero Matrix
• Identity Matrix
• Diagonal Matrix
I A = A I = A
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Basic Operations
• Addition, Subtraction, Multiplication
hdgc
fbea
hg
fe
dc
ba
hdgc
fbea
hg
fe
dc
ba
dhcfdgce
bhafbgae
hg
fe
dc
ba
Just add elements
Just subtract elements
Multiply each row by each column
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Multiplication
• Is AB = BA? Maybe, but maybe not!
• Is multiplication commutative?
......
...bgae
hg
fe
dc
ba
......
...fcea
dc
ba
hg
fe
42
31A
53
12B
Try for the 2 matrices below
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42
31A
53
12B
2216
1611
54123422
53113321
53
12
42
31BAC
Multiplication
Is AB = BA?
2913
104
45332513
41322112
42
31
53
12ABD
Multiplication is NOT commutative AB = BA
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Inverse of a Matrix
• Identity matrix: AI = A
• Some matrices have an inverse, such that:AA-1 = I
100
010
001
I
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Inverse of a 2x2 Matrix
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Matrix Inverse (Intro)
A A-1= A-1 A = I
I
100
010
001
71
00
051
0
0031
700
050
003
DD 1
Properties
A-1 only exists if A is square (n x n)
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Determinant of a 2x2 Matrix
• The determinant of the matrix A is denoted |A|.
• Matrix A has no inverse whenever |A|= 0.• A matrix with no inverse is SINGULAR.
42
31AE.g.
, so an inverse exists
26
13B
, so no inverse exists
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Inverse of a 2x2 Matrix
• AA-1 = I• If = 0, then A has no inverse
– A is SINGULAR
dc
baA
42
31AE.g.
12
34
2
11A
5.01
5.12
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Inverse of a 2x2 Matrix
• AA-1 = I• If |A| = 0, then A has no inverse
– A is SINGULAR
dc
baA
5.01
5.12
2344
5.15.132
10
01 The 2x2identity matrix