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082-Engineering-Mathematics-Anthony-Croft-Robert-Davison-Martin-Hargreaves-James-Flint-Edisi-5-2017

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8.5 Some special matrices 271

V new

= Rot(y,90 ◦ )Trans(1,2,3)V old

⎛ ⎞⎛

⎞ ⎛ ⎞

0010 2 5

= ⎜ 0100

⎟⎜5

⎝−1000⎠⎝5⎠ ⎜ 5

⎝−2⎠

0001 1 1

Hence

⎛ ⎞

5

r new

= ⎝ 5⎠

−2

8.5 SOMESPECIALMATRICES

8.5.1 Squarematrices

Amatrixwhichhasthesamenumberofrowsascolumnsiscalledasquarematrix.Thus

⎛ ⎞

123

( )

⎝−101⎠ −130

isasquare matrix, while isnot

241

321

8.5.2 Diagonalmatrices

Some square matrices have elements which are zero everywhere except on the leading

diagonal (top-lefttobottom-right). Such matrices aresaidtobediagonal. Thus

⎛ ⎞

⎛ ⎞

10 0 ( )

3000

⎝02 0⎠

1 0

⎜0200

0 b ⎝0010⎠

00−1

0000

areall diagonal matrices, whereas

⎛ ⎞

124

⎝010⎠

301

isnot.

8.5.3 Identitymatrices

Diagonal matrices which have only ones on their leading diagonals, for example

⎛ ⎞

( ) 100

1 0

and ⎝010⎠

0 1

001

arecalledidentity matrices and aredenoted by the letterI.

( ) ( )

1 0 2 44

Example8.14 FindIAwhereI = andA= and comment upon the result.

0 1 3−10

( )( ) ( )

1 0 2 44 2 44

Solution IA =

=

0 1 3−10 3−10

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