HP 39g+ - Manual (Page 184)

13-6 Matrices
To store one
element In HOME, enter, value matrixname(row,column).
For example, to change the element in the first row and
second column of M5 to 728, then display the resulting
matrix:
728
M5 1 2
M5
.
An attempt to store an element to a row or column beyond
the size of the matrix results in an error message.
Matrix arithmetic
You can use the arithmetic functions (+, –, ×, / ) with
matrix arguments. Division left-multiplies by the inverse of
the divisor. You can enter the matrices themselves or enter
the names of stored matrix variables. The matrices can be
real or complex.
For the next four examples, store [[1,2],[3,4]] into M1 and
[[5,6],[7,8]] into M2.
Example 1. Create the first matrix.
MATRIX
1 2
3 4
2. Create the second
matrix.
MATRIX
5 6
7
8