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The identity( Command

Command Summary Command Syntax Calculator Compatibility Token Size
Creates an n by n identity matrix. identity(n) TI-83/84/+/SE 1 byte

Press:
1. MATRX (on the 83) or 2ND MATRX (83+ or higher) to access the matrix menu.
2. LEFT to access the MATH submenu.
3. 5 to select identity(, or use arrows.

The identity( Command

The identity( command generates an identity matrix: that is, a matrix [B] such that for any other matrix [A], [A]*[B]=[A] (if [A] is the right size to make the multiplication valid).

The identity matrix is square (that is, the row dimension equals the column dimension); all of its elements are 0 except for the elements along the main diagonal (the diagonal going from top left to bottom right).

The command itself takes one argument: the size of the matrix, used for both row and column size, that is, identity(n) creates an n by n matrix.

:dim([A]
:identity(Ans(2→[B]
:[A][B]=[A]  // should always return 1, meaning 'true'

Optimization

The identity( command can be used as a quick way to create an empty square matrix: 0identity(n) will create an n by n matrix containing only 0 as an element. This is faster and smaller than the dim( and Fill( commands used for the same purpose:

:{5,5→dim([A]
:Fill(0,[A]
can be
:0identity(5→[A]

Error Conditions

  • ERR:INVALID DIM occurs if the size is not an integer 1-99. In practice, however, identity(21) is already too large for the calculator to generate.
  • ERR:MEMORY occurs if the size of the created matrix exceeds memory limits. This limit is hard-fixed to 3611 bytes (the size of a 20x20 matrix), regardless of having sufficient RAM to hold a larger matrix.
Authors: KG