Texas Instruments TI89 Developer Guide - Page 208
Other Constants, SV_SIGMA_X SYSVAR_TAG.
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166 Chapter 15: Expressions and The Expression Stack 15.2.4. The Operating System has system variables that are reserved for special purposes. These reserved variables are used in a variety of ways in graphing, plotting, table generation, and statistical computations. They are numbered and are represented as a SYSVAR_TAG on top of the corresponding system variable number. For example, the function graphing variable xmin is represented by SV_XMIN SYSVAR_TAG, and the statistics variable Σx is represented by SV_SIGMA_X SYSVAR_TAG. Two special naming conventions are associated with the underscore character '_'. Variable names that end with an underscore are assumed to be complex variables. Thus, the variable z is assumed to be real, but the variable z_ is assumed to be complex. Variable names that begin with an underscore are assumed to be unit names or the names of physical constants, which include a unit expression. For example, the unit meter is named _m, and the unit kilogram is named _kg. The physical constant for the speed of light is named _c and evaluates to the unit expression 299792458.0 _m / _s. Other Constants Arbitrary real constants @1, @2, . . . , and arbitrary integer constants @n1, @n2, . . . behave somewhat like variables and somewhat like constants. The number following the @ symbol (1, 2, etc.) is referred to as the "suffix." The representation uses ARB_REAL_TAG or ARB_INT_TAG on top of one quantum containing the identifying suffix. Thus, @25 is 25 ARB_REAL_TAG, and @n10 is 10 ARB_INT_TAG. The system also implements the following symbolic constants. Constant Type Boolean Boolean Finite Finite Finite Transfinite Transfinite Transfinite Transfinite Value TRUE FALSE π e (base of the natural ln) i (√(L1)) L 0/0 (any real value) Tag TRUE_TAG FALSE_TAG PI_TAG E_TAG I_TAG MINUS_INFINITY_TAG PLUS_INFINITY_TAG PLUS_OR_MINUS_INFINITY_TAG UNDEFINED_TAG Table 15.5: Symbolic Constants TI-89 / TI-92 Plus Developer Guide Not for Distribution Beta Version January 26, 2001
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