An elementary matrix is a square matrix that represents an elementary row operation. These matrices help us automate matrix transformations and decompositions.

Creation of an elementary matrix

To create an elementary matrix, En×nE_{n \times n}, we start with the identity matrix, In×nI_{n\times n}, and apply the desired elementary row operation to it. The resultant matrix is the elementary matrix corresponding to the given operation.

Row swap

An elementary matrix for row swap is an identity matrix with the two rows interchanged. These matrices are also called permutation matrices, represented by PijP_{ij}, where ii and jj represent the two rows to be swapped. For example, the elementary matrix to swap the second and third rows is as follows:

P23=[100001010]P_{23}=\begin{bmatrix} 1 & 0 & 0\\ 0 & 0 & 1\\ 0 & 1 & 0 \end{bmatrix}

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