HP (Hewlett-Packard) F2215AA#ABA ユーザーズマニュアル

You can not solve or integrate for unnamed variables or statistic registers.

Since the contents of I can change each time a program runs — or even in different 
parts of the same program — a program instruction such as STO (I) or (J) can store 
value to a different variable at different times. For example, STO(-1) indicates storing 
the value in Variable A. This maintains flexibility by leaving open (until the program 
runs) exactly which variable or program label will be needed. 

Indirect addressing is very useful for counting and controlling loops. The variable I

 

or J serves as an index, holding the address of the variable that contains the loop–
control number for the functions DSE and ISG. 

You can use (I) or (J) in an equation to specify a variable indirectly. Notice that 
 or  means the variable specified by the number in variable I or J (an 
indirect reference), but that I or J and or  (where the user parenthesis are 
used instead of the (I) or (J) key) means variable I or J.

Placing a positive number into variable I or J allows you to access up to 801 indirect 
variables. The following example indicates how to use them.

STO(I)/(J)
RCL(I)/(J)
STO +, –,

× ,÷, (I)/(J)

RCL +, –,

× ,÷, (I)/(J)

X<>(I)/(J)
FN=(I)/(J)

INPUT(I)/(J)
VIEW(I)/(J)
DSE(I)/(J)
ISG(I)/(J)
SOLVE(I)/(J)
∫ FN d(I)/(J)