Identity matrix

Definition

An identity matrix is a square matrix in which all the elements of the principal diagonal are ones, and all other elements are zeros. This special type of matrix acts as the multiplicative identity in matrix multiplication, meaning that when any matrix is multiplied by an identity matrix of compatible size, the original matrix remains unchanged. Identity matrices are essential in linear transformations, as they represent the transformation that leaves vectors unchanged.

5 Must Know Facts For Your Next Test

1. The identity matrix is denoted as I and can have dimensions like I_n for an n x n matrix.
2. For any matrix A of size m x n, multiplying it by an identity matrix I_n results in A (i.e., A * I_n = A).
3. The identity matrix serves as the equivalent of the number 1 in the world of matrices, maintaining other matrices when used in multiplication.
4. The size of the identity matrix must match the number of columns of the first matrix and rows of the second for multiplication to be valid.
5. In linear algebra, every invertible square matrix has an inverse that, when multiplied by the original matrix, results in the identity matrix.

Review Questions

• How does an identity matrix function within the context of linear transformations?
  • An identity matrix represents a linear transformation that leaves every vector unchanged. When applied to a vector or another matrix during a transformation process, it effectively does nothing to that vector or matrix. This characteristic makes the identity matrix crucial for understanding transformations, as it provides a baseline against which other transformations can be measured.
• Discuss how multiplying a given matrix by an identity matrix affects the original matrix and provide an example.
  • When a matrix A is multiplied by an identity matrix I of compatible dimensions, the result is simply A itself. For example, if A is a 2x2 matrix such as [[2, 3], [4, 5]] and I is also a 2x2 identity matrix [[1, 0], [0, 1]], then A * I = [[2, 3], [4, 5]]. This property demonstrates how the identity matrix functions similarly to the number one in regular multiplication.
• Evaluate the significance of the identity matrix in determining whether other matrices are invertible.
  • The identity matrix plays a crucial role in identifying invertible matrices since a square matrix A is invertible if there exists another square matrix B such that A * B = I (the identity matrix). This relationship indicates that A can be 'undone' by B. Thus, when working with systems of linear equations or transformations, recognizing this relationship helps determine whether solutions exist and how they can be efficiently calculated.

Related terms

Square Matrix: A square matrix is a matrix with the same number of rows and columns, essential for defining concepts like identity matrices.

Matrix Multiplication: Matrix multiplication is a binary operation that produces a new matrix by combining two matrices according to specific rules, including interactions with identity matrices.

Linear Transformation: A linear transformation is a function between two vector spaces that preserves the operations of vector addition and scalar multiplication, often represented using matrices.