HP 15c - Manual (Page 146)

146 Section 12: Calculating with Matrices
Using R
0
and R
1
. To access a particular matrix element, store its row
number in R
0
and its column number in R
1
. These numbers won't change
automatically (unless the calculator is in User mode).

To recall the element value (after storing the row and column
numbers), press l followed by the letter key specifying the
matrix.

To store a value in that element (after storing the row and column
numbers), place the value in the X-register and press O
followed by the letter key specifying the matrix.
Example: Store the value 9 as the element in row 2, column 3 of matrix A
from the previous example.
Keystrokes Display
2
O 0 2.0000
Stores row number in R
0
.
3
O 1 3.0000
Stores column number in R
1
.
9
9
Keys the new element value into
the X-register.
O A A 2,3
Row 2, column 3 of A.
9.0000
Value of a
23
.
Using the Stack. You can use the stack registers to specify a particular matrix
element. This eliminates the need to change the numbers in R
0
and R
1
.

To recall an element value, enter the row number and column
number into the stack (in that order). Then press l |
followed by the letter key specifying the matrix. The element value
is placed in the X-register. (The row and column numbers are lost
from the stack.)

To store an element value, first enter the value into the stack
followed by the row number and column number. Then press
O | followed by the letter key specifying the matrix. (The
row and column numbers are lost from the stack; the element value
is returned to the X-register.)
Note that these are the only operations in which the blue | key precedes
a gold letter key.