Ifft - HP 48gII Advanced User's Reference Manual

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Error trapping structures enable program execution to continue after a "trapped" error occurs.
• IFERR ... THEN ... END executes a sequence of commands if an error occurs. The syntax
of IFERR ... THEN ... END is:
IFERR trap-clause THEN error-clause END
If an error occurs during execution of the trap clause:
The error is ignored.
1
The remainder of the trap clause is discarded.
2
The key buffer is cleared.
3
If any or all of the display is "frozen" (by FREEZE), that state is cancelled.
4
If Last Arguments is enabled, the arguments to the command that caused the error are
5
returned to the stack.
Program execution jumps to the error clause.
6
The commands in the error clause are executed only if an error is generated during execution
of the trap clause.
• IFERR ... THEN ... ELSE ... END executes one sequence of commands if an error occurs
or another sequence of commands if an error does not occur. The syntax of IFERR ...
THEN ... ELSE ... END is:
IFERR trap-clause THEN error-clause ELSE normal-clause END
If an error occurs during execution of the trap clause, the same six events listed above occur.
If no error occurs, execution jumps to the normal clause at the completion of the trap clause.
!°LL
Access:
Flags:
Last Arguments (-55)
Input/Output: None
See also:
CASE, ELSE, END, IF, THEN

IFFT

Type:
Command
Description: Inverse Discrete Fourier Transform Command: Computes the one- or two-dimensional inverse
discrete Fourier transform of an array.
If the argument is an N-vector or an N × 1 or 1 × N matrix, IFFT computes the one-
dimensional inverse transform. If the argument is an M × N matrix, IFFT computes the two-
dimensional inverse transform. M and N must be integral powers of 2.
The one-dimensional inverse discrete Fourier transform of an N-vector Y is the N-vector X
where:
for n = 0, 1, ..., N – 1.
The two-dimensional inverse discrete Fourier transform of an M × N matrix Y is the M × N
matrix X where:
for m = 0, 1, ..., M – 1 and n = 0, 1, ..., N – 1.
The discrete Fourier transform and its inverse are defined for any positive sequence length.
However, the calculation can be performed very rapidly when the sequence length is a power of
3-82 Full Command and Function Reference
[
]
ERROR
IFERR
IFERR
2 ikn
N 1
-------------- -
1
X
=
--- -
Y
e
n
k
N
k
=
0
M 1
N 1
1
X
=
Y
e
-------- -
mn
kl
MN
k
=
0
l
=
0
( °is the left-shift of the Nkey).
N
i
=
1
2 i km
2 i ln
--------------- -
----------------- -
M
N
e
i
=
1

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