5. Let 0-2 1 -1 2-2 30 21 45 -4 4 -7 1 Find a PLU-factorization of A, and use it to solve the linear system Ar = b. A= b= 21 6 9 -20

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Chapter2: Second-order Linear Odes
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5. Let
30
2 1
45
-4 4 -7 1
Find a PLU-factorization of A, and use it to solve the linear system Az = b.
0-2
1 -1
2-2
A
21
6
9
-20
Transcribed Image Text:5. Let 30 2 1 45 -4 4 -7 1 Find a PLU-factorization of A, and use it to solve the linear system Az = b. 0-2 1 -1 2-2 A 21 6 9 -20
Expert Solution
Step 1: Find the PLU factorization of A

We have, 

A equals open square brackets table row 0 cell negative 2 end cell 3 0 row 1 cell negative 1 end cell 2 1 row 2 cell negative 2 end cell 4 5 row cell negative 4 end cell 4 cell negative 7 end cell 1 end table close square brackets

Start from identity matrix L equals open square brackets table row 1 0 0 0 row 0 1 0 0 row 0 0 1 0 row 0 0 0 1 end table close square brackets and identity permutation matrix P equals open square brackets table row 1 0 0 0 row 0 1 0 0 row 0 0 1 0 row 0 0 0 1 end table close square brackets

A p p l y i n g space R subscript 1 left right arrow R subscript 2
open square brackets table row 1 cell negative 1 end cell 2 1 row 0 cell negative 2 end cell 3 0 row 2 cell negative 2 end cell 4 5 row cell negative 4 end cell 4 cell negative 7 end cell 1 end table close square brackets space space space space space S o comma space P equals open square brackets table row 0 1 0 0 row 1 0 0 0 row 0 0 1 0 row 0 0 0 1 end table close square brackets
R subscript 3 rightwards arrow R subscript 3 minus 2 cross times R subscript 1
A equals open square brackets table row 1 cell negative 1 end cell 2 1 row 0 cell negative 2 end cell 3 0 row 0 0 0 3 row cell negative 4 end cell 4 cell negative 7 end cell 1 end table close square brackets space space space space S o comma space L equals open square brackets table row 1 0 0 0 row 0 1 0 0 row 2 0 1 0 row 0 0 0 1 end table close square brackets
R subscript 4 rightwards arrow R subscript 4 minus open parentheses negative 4 close parentheses cross times R subscript 1
open square brackets table row 1 cell negative 1 end cell 2 1 row 0 cell negative 2 end cell 3 0 row 0 0 0 3 row 0 0 1 5 end table close square brackets space space space space space S o comma space L equals open square brackets table row 1 0 0 0 row 0 1 0 0 row 2 0 1 0 row cell negative 4 end cell 0 0 1 end table close square brackets
R subscript 3 left right arrow R subscript 4
U equals open square brackets table row 1 cell negative 1 end cell 2 1 row 0 cell negative 2 end cell 3 0 row 0 0 1 5 row 0 0 0 3 end table close square brackets space space space space space S o comma space P equals open square brackets table row 0 1 0 0 row 1 0 0 0 row 0 0 0 1 row 0 0 1 0 end table close square brackets space a n d space L equals open square brackets table row 1 0 0 0 row 0 1 0 0 row cell negative 4 end cell 0 1 0 row 2 0 0 1 end table close square brackets
T h e r e f o r e space P L U thin space f a c t o r i z a t i o n space o f space A space i s space
P A equals L U

Here, L is the multipliers used in the elimination with 1 on its diagonal.  

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