Is_Variable - Texas Instruments TI-89 Developer's Manual

Appendix A: System Routines — Variable Name Utilities

is_variable

Declaration: Boolean is_variable (EStackIndex i )
Category(ies): Variable Name Utilities, Algebra Utilities
Description: Determines whether i indexes a subscripted or unsubscripted variable.
Inputs: i
Outputs: Returns TRUE if i indexes a subscripted or unsubscripted variable.
Assumptions: None
Side Effects: None
Availability: On AMS 2.00 and higher.
TI-89 / TI-92 Plus
Differences: None
See Also: is_complex_number, is_constant
Example:
Boolean is_rational_expression (EStackIndex i)
/* i indexes an expression.
Returns TRUE if it is a rational expression in all of its variables.
Otherwise returns FALSE.
*/
{ EStackIndex j;
for (;;)
if (IS_NUMBER_OR_VARIABLE_TAG (ESTACK (i)) || is_variable (i))
return TRUE;
else if (ADD_TAG == ESTACK (i) || MULTIPLY_TAG == ESTACK (i))
if (is_rational_expression (--i))
i = next_expression_index (i);
else
return FALSE;
else if (EXPONENTIATION_TAG == ESTACK (i))
{ j = next_expression_index (--i);
if (! IS_INTEGER_TAG (ESTACK (j)))
return is_constant (i);
}
else
return is_constant (i);
}
TI-89 / TI-92 Plus Developer Guide
— Index of the top tag of an internally-simplified expression.
Not for Distribution
1121
Beta Version January 26, 2001