HP 40G manual Home, Symbolic calculations in the Function aplet, Using formal variables

Symbolic calculations

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Using formal variables

Symbolic calculations in the Function aplet

The HP 39G/40G has the ability to perform symbolic calculations, for example, symbolic integration and differentiation. You can perform symbolic calculations in HOME and in the Function aplet.

When you perform calculations that contain normal variables, the calculator substitutes values for any variables. For example, if you enter A+B on the command line and press￿ >(17(5@, the calculator retrieves the values for A and B from memory and substitutes them in the calculation.

To perform symbolic calculations, for example symbolic differentiations and integrations, you need to use formal names. The HP 39G/40G has six formal names available for use in symbolic calculations. These are S0 to S5. When you perform a calculation that contains a formal name, the

HP 39G/40G does not carry out any substitutions.

You can mix formal names and real variables. Evaluating (A+B+S1)2 will evaluate A+B, but not S1.

If you need to evaluate an expression that contains formal names numerically, you use the (where) command, listed in the Math menu under the Symbolic category.

For example to evaluate (S1*S2)2 when S1=2 and S2=4, you would enter the calculation as follows:

(The symbol is in the CHARS menu: press >6+,)7@CHARS. The = sign is listed in the MATH menu under Symbolic functions.)

You can perform symbolic operations in the Function aplet’s Symbolic view. For example, to find the derivative of a function in the Function aplet’s Symbolic view, you define two functions and define the second function as a derivative of the first function. You then evaluate the second function. See “To find derivatives in the Function aplet’s Symbolic view” on page 10-24 for an example.

10-22 Using mathematical functions