Texas Instruments TI-83 PLUS - Manual (Page 269)

TI-83 Plus Matrices 266
5. Repeat steps 2 through 4 to enter all of the rows.
6. Press y [ ] ] to indicate the end of the matrix.
Note: The closing ]] are not necessary at the end of an expression or
preceding ! .
The resulting matrix is displayed in the form:
[[ element1,1 , ... , element1,n ], ... ,[ elementm,1 , ... , elementm,n ]]
Any expressions are evaluated when the entry is executed.
Note: The commas that you must enter to separate elements are not
displayed on output.