Texas Instruments TI-83 Plus Manual Book page 34

Use options on this screen ... To do this:
MAIN displays the main menu.
BACK displays the matrix entry screen so
that you can view or change the values.
STORE RREF stores the reduced row-
echelon form of a matrix to a matrix
RREF screen
variable that you select.
TI-83 Plus Polynomial Root Finder / Simultaneous Equation Solver Application Page 34