Math Problem Statement

Construct the QR decomposition of the following matrix: A = [ [1, 0, 0], [1, 1, 0], [1, 1, 1], [1, 1, 1] ] (4x3 matrix)

Solution

The image shows a request to construct the QR decomposition of a given matrix. The matrix provided is:

A=[100110111111]A = \begin{bmatrix} 1 & 0 & 0 \\ 1 & 1 & 0 \\ 1 & 1 & 1 \\ 1 & 1 & 1 \end{bmatrix} This is a 4×34 \times 3 matrix.

QR Decomposition Overview:

QR decomposition of a matrix AA is a factorization of the matrix into an orthogonal matrix QQ and an upper triangular matrix RR, such that: A=QRA = QR Where:

  • QQ is an orthogonal matrix (QTQ=IQ^T Q = I).
  • RR is an upper triangular matrix.

Steps to Solve:

  1. Apply the Gram-Schmidt process to the columns of AA to obtain the orthogonal vectors that form the matrix QQ.
  2. Normalize the orthogonal vectors to make them orthonormal, ensuring that the columns of QQ are orthonormal.
  3. The matrix RR is then calculated by projecting the original columns of AA onto the orthogonal vectors.

Let me now calculate the QR decomposition of the given matrix.

The QR decomposition of the matrix

A=[100110111111]A = \begin{bmatrix} 1 & 0 & 0 \\ 1 & 1 & 0 \\ 1 & 1 & 1 \\ 1 & 1 & 1 \end{bmatrix}

results in:

  1. The orthogonal matrix QQ is:
-0.5 & 0.866 & 0 \\ -0.5 & -0.289 & 0.816 \\ -0.5 & -0.289 & -0.408 \\ -0.5 & -0.289 & -0.408 \end{bmatrix}$$ 2. The upper triangular matrix $$R$$ is: $$R = \begin{bmatrix} -2 & -1.5 & -1 \\ 0 & -0.866 & -0.577 \\ 0 & 0 & -0.816 \end{bmatrix}$$ This decomposition satisfies $$A = QR$$. Would you like further details on how to compute this step-by-step? Here are five related questions to consider: 1. What is the Gram-Schmidt process, and how is it used to form the $$Q$$ matrix? 2. How do we determine if a matrix is orthogonal? 3. Can the QR decomposition be used to solve systems of linear equations? 4. How does the QR algorithm assist in finding eigenvalues of a matrix? 5. What are the applications of QR decomposition in numerical methods? **Tip:** QR decomposition is especially useful for solving least squares problems where you need to minimize the error in approximations!

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Math Problem Analysis

Mathematical Concepts

Linear Algebra
Matrix Decomposition
QR Decomposition

Formulas

A = QR
Q^T Q = I (Orthogonal Matrix)
R (Upper Triangular Matrix)

Theorems

Gram-Schmidt Process

Suitable Grade Level

University Level