Kronecker Product Exercise

By: Prof. Dr. Fazal Rehman | Last updated: February 6, 2025

\[\] \[ \textbf{Q#1: Compute the Kronecker Product of the following matrices:} \] \[ A = \begin{pmatrix} 1 & 2 \\ 3 & 4 \end{pmatrix}, \quad B = \begin{pmatrix} 0 & 5 \\ 6 & 7 \end{pmatrix} \] \[ \textbf{Step 1: Use the formula for the Kronecker product.} \] \[ A \otimes B = \begin{pmatrix} a_{11}B & a_{12}B \\ a_{21}B & a_{22}B \end{pmatrix} \] \[ \textbf{Where each element of } A \textbf{ is multiplied by the entire matrix } B. \] \[ \textbf{Step 2: Substitute the values of } A \textbf{ and } B. \] \[ A \otimes B = \begin{pmatrix} 1 \cdot \begin{pmatrix} 0 & 5 \\ 6 & 7 \end{pmatrix} & 2 \cdot \begin{pmatrix} 0 & 5 \\ 6 & 7 \end{pmatrix} \\ 3 \cdot \begin{pmatrix} 0 & 5 \\ 6 & 7 \end{pmatrix} & 4 \cdot \begin{pmatrix} 0 & 5 \\ 6 & 7 \end{pmatrix} \end{pmatrix} \] \[ \textbf{Step 3: Multiply each element.} \] \[ A \otimes B = \begin{pmatrix} \begin{pmatrix} 0 & 5 \\ 6 & 7 \end{pmatrix} & \begin{pmatrix} 0 & 10 \\ 12 & 14 \end{pmatrix} \\ \begin{pmatrix} 0 & 15 \\ 18 & 21 \end{pmatrix} & \begin{pmatrix} 0 & 20 \\ 24 & 28 \end{pmatrix} \end{pmatrix} \] \[ \textbf{Step 4: Combine into a single matrix.} \] \[ A \otimes B = \begin{pmatrix} 0 & 5 & 0 & 10 \\ 6 & 7 & 12 & 14 \\ 0 & 15 & 0 & 20 \\ 18 & 21 & 24 & 28 \end{pmatrix} \] \[ \textbf{Solution for Q1:} \] \[ A \otimes B = \begin{pmatrix} 0 & 5 & 0 & 10 \\ 6 & 7 & 12 & 14 \\ 0 & 15 & 0 & 20 \\ 18 & 21 & 24 & 28 \end{pmatrix} \]
\[ \textbf{Q#2: Compute the Kronecker Product of the following matrices:} \] \[ A = \begin{pmatrix} 2 & 3 \end{pmatrix}, \quad B = \begin{pmatrix} 4 & 5 \\ 6 & 7 \end{pmatrix} \] \[ \text{Find } A \otimes B. \] \[ \textbf{Step 1: Formula for Kronecker Product} \] The Kronecker Product of \( A \otimes B \) is defined as: \[ A \otimes B = \begin{pmatrix} a_{11}B & a_{12}B \end{pmatrix} \] Here, \( A \) has \( 1 \times 2 \) dimensions, and \( B \) has \( 2 \times 2 \) dimensions. The resulting matrix will have dimensions: \[ (1 \times 2) \otimes (2 \times 2) = 2 \times 4 \] \[ \textbf{Step 2: Compute \( a_{ij} \cdot B \)} \] \[ \textbf{Compute } a_{11}B = 2 \cdot B: \] \[ a_{11}B = 2 \cdot \begin{pmatrix} 4 & 5 \\ 6 & 7 \end{pmatrix} = \begin{pmatrix} 8 & 10 \\ 12 & 14 \end{pmatrix} \] \[ \textbf{Compute } a_{12}B = 3 \cdot B: \] \[ a_{12}B = 3 \cdot \begin{pmatrix} 4 & 5 \\ 6 & 7 \end{pmatrix} = \begin{pmatrix} 12 & 15 \\ 18 & 21 \end{pmatrix} \] \[ \textbf{Step 3: Assemble the Resulting Matrix} \] Now combine the computed blocks \( a_{11}B \) and \( a_{12}B \) to form \( A \otimes B \): \[ A \otimes B = \begin{pmatrix} a_{11}B & a_{12}B \end{pmatrix} \] Substitute the blocks: \[ A \otimes B = \begin{pmatrix} 8 & 10 & 12 & 15 \\ 12 & 14 & 18 & 21 \end{pmatrix} \] \[ \textbf{Final Answer:} \] \[ A \otimes B = \begin{pmatrix} 8 & 10 & 12 & 15 \\ 12 & 14 & 18 & 21 \end{pmatrix} \]

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