I. Basic Keys

    C. Other Keys

8. STO (store): Storing Variables, Creating Folders, User-Defined Functions

The store key, , can be used to store the value of a single variable or a user-defined function. User-defined functions can save you a lot of time when you need to repeat the same expression with different values several times.

Example: Store the value 3.456 to the variable x and then evaluate the expressions

Enter 3.456 X and .
Press , the expression, and .
Press , the expression, and .

The value of x will remain the same until you clear it or change it. However, it will not affect graphs.

The next examples show you how to create user-defined functions. You can enter as many expressions as you need. The expression can contain as many expressions as necessary. You should create unique names that not be used in the arguments for other functions or programs.

The arguments represent whatever values to pass to the function. They are just placeholders, like in any function. These can be created using one of two methods. Both are illustrated below.

Example: Create a function named tiger that evaluates the sum of a value raised to the 4th power and the x root of that value. It will follow the format: Function name (Argument list)=Definition.

Using Define command
Enter the function.

Use the function just like any other function. You can evaluate it alone or in another expression.

Press [VAR-LINK].
Scroll down to the function.
Press to call up the function.
Enter the values 3 and 7.
To get a decimal approximation,
enter as shown with a
decimal point included.
Take the square root of the
function tiger(2,3.).

The TI-89 has one built-in folder. It is called MAIN. All variables are stored in this folder. You can organize your user-defined variables and functions by creating additional folders. You can store a user-defined variable or function in any folder. However, you cannot move a variable with a reserved name or a system variable to a folder other than MAIN. Folders can store separate sets of variables with the same names but different values.

If you look at the screen below, you will see the word MAIN in the lower left corner. This indicates that MAIN is the current folder.

The easiest way to create a folder is via the home screen. When you create a new folder, it will automatically be set as the current folder.

Example: Create a folder named lsu from the home screen.

Press and scroll down
to B:NewFold.
Type in lsu and press .
Notice that lsu is now
the current folder.

Example: Copy the function tiger to the folder lsu.

Press [VAR-LINK].
Scroll down and select tiger.
Press and 2:Copy
Press .
Press . The function tiger
is now in the lsu folder.

Example: Change the folder back to MAIN.

Press .
Scroll to current folder
and then right .
Press .
Press . MAIN is now
the current folder.



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