Find an LU factorization of the matrix A (with L unit lower triangular). 6 4 A= 12 5

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Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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## Finding LU Factorization of a Matrix (with L unit lower triangular)

### Problem Statement
Find an LU factorization of the matrix \( A \) where \( L \) is a unit lower triangular matrix.

The matrix \( A \) is given by:
\[ 
A = \begin{pmatrix} 
6 & 4 \\
12 & 5 
\end{pmatrix} 
\]

### Explanation
LU factorization of a matrix involves decomposing the matrix \( A \) into two matrices: \( L \) and \( U \).

- \( L \) is a lower triangular matrix with ones on the diagonal.
- \( U \) is an upper triangular matrix.

In this case, since \( L \) is a unit lower triangular matrix, it will have ones on the diagonal. The goal is to express \( A \) in the form \( A = LU \), where:
\[ 
L = \begin{pmatrix} 
1 & 0 \\
l_{21} & 1 
\end{pmatrix} 
\]
\[ 
U = \begin{pmatrix} 
u_{11} & u_{12} \\
0 & u_{22} 
\end{pmatrix} 
\]

Let's find the values of \( l_{21} \), \( u_{11} \), \( u_{12} \), and \( u_{22} \).

1. **Determine \( u_{11} \):**
   From the first row of \( A \), we have:
   \[ 
   u_{11} = 6 
   \]
   
2. **Determine \( u_{12} \):**
   Continuing from the first row of \( A \), we get:
   \[ 
   u_{12} = 4 
   \]

3. **Determine \( l_{21} \):**
   From the second row of \( A \), since \( l_{21} \times u_{11} = 12 \), we have:
   \[ 
   l_{21} = \frac{12}{6} = 2 
   \]

4. **Determine \( u_{22} \):**
   From the second row of \( A \), substituting known values:
   \[ 
   2 \times 4 + u_{22} = 5 \Rightarrow u_{22} = 5 -
Transcribed Image Text:## Finding LU Factorization of a Matrix (with L unit lower triangular) ### Problem Statement Find an LU factorization of the matrix \( A \) where \( L \) is a unit lower triangular matrix. The matrix \( A \) is given by: \[ A = \begin{pmatrix} 6 & 4 \\ 12 & 5 \end{pmatrix} \] ### Explanation LU factorization of a matrix involves decomposing the matrix \( A \) into two matrices: \( L \) and \( U \). - \( L \) is a lower triangular matrix with ones on the diagonal. - \( U \) is an upper triangular matrix. In this case, since \( L \) is a unit lower triangular matrix, it will have ones on the diagonal. The goal is to express \( A \) in the form \( A = LU \), where: \[ L = \begin{pmatrix} 1 & 0 \\ l_{21} & 1 \end{pmatrix} \] \[ U = \begin{pmatrix} u_{11} & u_{12} \\ 0 & u_{22} \end{pmatrix} \] Let's find the values of \( l_{21} \), \( u_{11} \), \( u_{12} \), and \( u_{22} \). 1. **Determine \( u_{11} \):** From the first row of \( A \), we have: \[ u_{11} = 6 \] 2. **Determine \( u_{12} \):** Continuing from the first row of \( A \), we get: \[ u_{12} = 4 \] 3. **Determine \( l_{21} \):** From the second row of \( A \), since \( l_{21} \times u_{11} = 12 \), we have: \[ l_{21} = \frac{12}{6} = 2 \] 4. **Determine \( u_{22} \):** From the second row of \( A \), substituting known values: \[ 2 \times 4 + u_{22} = 5 \Rightarrow u_{22} = 5 -
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