HP 40gs hp 40gs_user's guide_English_E_HDPMSG40E07A.pdf - Page 187

hp40g+.book Page 5 Friday, December 9, 2005 1:03 AM CAS modes The modes that determine how CAS operates can be set on CAS MODES screen. To display CAS MODES screen, press: NOTE ·To navigate through the options in CAS MODES screen, press the arrow keys. To select or deselect a mode, navigate to the appropriate field and press until the correct setting is displayed (indicated by a check mark in the field). For some settings (such as INDEP VAR and MODULO), you will need to press to be able to change the setting. Press to close CAS MODES screen. You can also set CAS modes from within the Equation Writer. See "Configuration menus" on page 15-3 for information. Selecting the independent variable Selecting the modulus Approximate vs. Exact mode Many of the functions provided by CAS use a pre- determined independent variable. By default, that variable is the letter X (upper case) as shown in CAS MODES screen above. However, you can change this variable to any other letter, or combination of letters and numbers, by editing the INDEP VAR field in CAS MODES screen. To change the setting, press , enter a new value and then press . The variable VX in the calculator's {HOME CASDIR} directory takes, by default, the value of 'X'. This is the name of the preferred independent variable for algebraic and calculus applications. If you use another independent variable name, some functions (for example, HORNER) will not work properly. The MODULO option on CAS MODES screen lets you specify the modulo you want to use in modular arithmetic. The default value is 13. When the APPROX mode is selected, symbolic operations (for example, definite integrals, square roots, etc.), will be calculated numerically. When this mode is unselected, exact mode is active, hence symbolic operations will be Computer Algebra System (CAS) 14-5