Texas Instruments TI89 Developer Guide - Page 274

232 Appendix A: System Routines - Algebra Utilities compare_expressions Declaration: Category(ies): Description: Inputs: Outputs: Assumptions: Side Effects: Availability: int compare_expressions (EStackIndex i, EStackIndex j) Algebra Utilities Returns an int that is 0 if expressions indexed by i and j are equal in the sense that they have the same structure, variables, function names, and numbers that "compare equal." A float and a rational number "compare equal" if converting the rational number to a float produces an identical number. Otherwise returns a positive int if expression indexed by i is more main, or returns a negative int if the expression indexed by i is less main. Glossing over details, variables are more main than symbolic constants such as p, which are more main than numbers. If the user enters an expression such as expand ( . . . , var) or integral ( . . . , var), then that variable is most main. Otherwise, the 26 Roman 1-letter variables order r>s> . . . >z>a>b> . . . >q, which order more main than all other variables, which order alphabetically. Functions and operators are typically ordered by recursively comparing their first arguments, with ties broken by comparing their second arguments, etc., then finally comparing the operators or functions, if necessary. Examples: i indexes j indexes Compare expression returns L2.0 L2 0 L2.0 L1 L1 p 4 1 x 4 1 x r L1 x ln(y) 1 x ln(x) L1 i, j - Indices of the top tags of internally-simplified expressions. Returns an int that is 0 if expressions indexed by i and j are equal in the sense that they have the same structure, variables, function names, and numbers that "compare equal." None None All versions of the TI-89 / TI-92 Plus. (continued) TI-89 / TI-92 Plus Developer Guide Not for Distribution Beta Version January 26, 2001