Reference Guide

3-114 Full Command and Function Reference
Access: !´L FFT IFFT ( ´ is the left-shift of the Pkey).
Input/Output:
Level 1/Argument 1 Level 1/Item 1
[ array ]
1
→
[ array ]
2
See also: FFT
IFT
Type: Command
Description: IF-THEN Command: Executes obj if T/F is nonzero. Discards obj if T/F is zero.
IFT lets you execute in stack syntax the decision-making process of the IF … THEN … END
conditional structure. The “true clause” is obj in argument 2 (level 1).
Access: !° BRANCH IFT ( °is the left-shift of the Nkey).
Input/Output:
Level 2/Argument 1 Level 1/Argument 2 Level 1/Item 1
T/F obj
→
It depends!
Example: « X 0 > "Positive" IFT » puts "Positive" in level 1 if X contains a positive
real number.
See also: IFTE
IFTE
Type: Function
Description: IF-THEN-ELSE Function: Executes the obj in argument 2 or level 2 if T/F is nonzero. Executes
the obj in argument 3 or level 1 if T/F is zero.
IFTE lets you execute in stack syntax the decision-making process of the IF … THEN … ELSE
… END conditional structure. The “true clause” is obj
true
in argument 2 or level 2. The “false
clause” is obj
false
in argument 3 or level 1.
IFTE is also allowed in algebraic expressions, with the following syntax:
IFTE( test,true-clause,false-clause )
When an algebraic containing IFTE is evaluated, its first argument test is evaluated to a test result.
If it returns a nonzero real number, true-clause is evaluated. If it returns zero, false-clause is evaluated.
Access: !° BRANCH L IFTE ( °is the left-shift of the Nkey).
Input/Output:
Level 3/Argument 1 Level 2/Argument 2 Level 1/Argument 3 Level 1/Item 1
T/F obj
true
obj
false
→
It depends!
Example 1: The command sequence X 0 Š "Positive" "Negative" IFTE leaves
"Positive" on the stack if X contains a non-negative real number, or "Negative" if
X contains a negative real number.
Example 2: The algebraic 'IFTE(X‹0,SIN(X)/X,1)' returns the value of sin(x)/x, even for x = 0,
which would normally cause an Infinite Result error.
See also: IFT
ILAP
Type: Function
Description: Returns the inverse Laplace transform of an expression. The expression must evaluate to a
rational fraction.