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Computer Algebra System
CAS SettingsSelecting CAS SettingsCAS settings are selected using the CAS MODES input form, described in Chapter 1 of the User’s Manual. Selecting a mode is equivalent to setting or clearing one of the system flags, the flag numbers are given in the “Flags” part of the operation descriptions.
Pressing the Lkey in the CAS MODES input form displays a menu that allows the user to calculate settings. For
example, if the Modulo field is selected in the CAS MODES form, and Lis pressed, the following menu keys are available.
!TYPES lists the types of object that can be chosen for this setting. For the modulo, this can be a real number or an integer. For checked mode settings, this can only be a real number; if it is zero the mode is unchecked, if it is anything else the mode is checked.
!CALC lets the user calculate a value for the setting, for example a new value for the modulo setting can be calculated.
The !STS! menu key allows the user to switch the heading lines between the “CAS MODES” heading and the normal heading lines, so that the user can see what the current settings are while carrying out a calculation.
!RESET allows the setting to be reset to its default value, or all CAS settings to be reset to their default values.
See Appendix C in the User’s Guide for further details of the CAS settings, and for other information about the CAS. Information on the Help system of the CAS is provided in Appendix C and also in Appendix H of the User’s Guide.
The CAS directory, CASDIRCAS settings are stored as flag settings, and as variables in the CASDIR directory, which is automatically created as a subdirectory of the HOME directory. Variables in this directory include:
VX: A name or list of names of the current CAS variable or variables. Default value is X
MODULO: The current modulus used for CAS modulo operations. Default value is 13, but is reset to 3 by the !RESET key in the CAS menu.
PERIOD: The period for CAS periodic operations, 2π by default.
EPS: The value chosen such that coefficients in a polynomial smaller than this value are replaced with 0 by the EPSX0 command.
REALASSUME: A list of the names of variables that some CAS operations treat as real numbers when complex mode is set. If additional assumptions are made on any variables, these are included here. By default the list is {X, Y, t, S1, S2}.
PRIMIT: Temporary storage of
MATRIX: Temporary storage of a matrix used during CAS operations.
CASINFO: Temporary storage of graphic display during
The CAS is a powerful tool, and part of that power lies in the many modes and settings available. This means that if a setting is wrong then the CAS can give unexpected results or error messages. The following points should be observed. If an unexpected error occurs, or an unexpected message is seen, check this list.
Computer Algebra System