Math 2.0

object

Identity matrix

Description

Let RR be a ring and let n≥0n \ge 0 be an integer. The identity matrix InI_n is the n×nn \times n matrix over RR with entries 11 on the main diagonal and 00 elsewhere. Its entries are (In)ij=δij(I_n)_{ij} = \delta_{ij}, where δij=1\delta_{ij} = 1 if i=ji = j and δij=0\delta_{ij} = 0 otherwise. For each m×nm \times n matrix AA, AIn=AA I_n = A and ImA=AI_m A = A.

Remarks

The identity matrix InI_n is the identity element of the matrix ring Mn(R)M_n(R). It is the matrix of the identity map in any basis. For example, I2=(1001)I_2 = \begin{pmatrix} 1 & 0 \\ 0 & 1 \end{pmatrix}.

Explanations

L1 human

The identity matrix has ones on the diagonal and zeros everywhere else. It plays the role of the number 11: multiplying by it changes nothing. As a map, it leaves each vector where it is.

What this node needs for W2
  • section Invariants: a table of the main invariants (0 of 1)

The writing levels say how complete the text of a node is. They do not measure its truth.

What depends on this

83 nodes use this node, directly or through other nodes.

Sources

  1. Web https://en.wikipedia.org/wiki/Identity_matrix, lead section