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The 21 pages that link to Identity matrix, each with the reason it gives.
EigenvalueRelated: Subtracting a scalar multiple of it forms the matrix used to test eigenvalues.
Matrix multiplicationRelated: Multiplying by it leaves a compatible matrix unchanged.
Characteristic polynomialRelated: It makes λI − A a matrix whose determinant defines the polynomial.
Invertible matrixRelated: An inverse is defined by multiplying to this matrix.
Orthogonal matrixRelated: Multiplying an orthogonal matrix by its transpose gives the identity.
OneRelated: Its diagonal entries are one, preserving vectors under matrix multiplication.
Kronecker deltaRelated: Its entries are precisely the Kronecker delta values.
Cramer's ruleRelated: The inverse condition is defined by multiplication producing this matrix.
Laplace expansionRelated: Its sparse rows and columns make determinant expansions immediate.