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identity matrix

$I_n$ — 1s on the diagonal, 0s elsewhere; the matrix analogue of 1.

The identity matrix of size $n$ , written $I_n$ , is the $n\times n$ matrix with $1$ s down the main diagonal and $0$ s everywhere else. It is the matrix analogue of the number $1$ : for any matrix $A$ whose shape makes the product defined, $I_mA=A$ and $AI_n=A$ .

See also

diagonal matrix inverse

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