TI-BASIC:Identity
Command Summary
Creates an n by n identity matrix.
Command Syntax
identity(n)
Menu Location
Press:
- MATRX (on the 83) or 2ND MATRX (83+ or higher) to access the matrix menu.
- LEFT to access the MATH submenu.
- 5 to select identity(, or use arrows.
TI-83/84/+/SE
1 byte
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, even identity(37 requires more free RAM than the calculator ever has.
