HP 15c - Manual (Page 176)

176 Section 12: Calculating with Matrices
Using Matrix Operations in a Program
If the calculator is in User mode during program entry when you enter a
O or l{A through E, %} instruction to store or recall a
matrix element, a u replaces the dash usually displayed after the line
number. When this line is executed in a running program, it operates as
though the calculator were in User mode. That is, the row and column
numbers in R
0
and R
1
are automatically incremented according to the
dimensions of the specified matrix. This allows you to access elements
sequentially. (The USER annunciator has no effect during program
execution.)
In addition, when the last element is accessed by the ―User‖ O or l
instruction – when R
0
and R
1
are returned to 1 – program execution skips
the next line. This is useful for programming a loop that stores or recalls
each matrix element, then continues executing the program. For example,
the following sequence squares all elements of matrix D: