Brigham E O (1974) The Fast Fourier Transform Prentice–Hall
Temperton C (1983) Fast mixed-radix real Fourier transforms J. Comput. Phys.52 340–350
1: – IntegerInput
On entry: , the first dimension of the transform.
2: – IntegerInput
On entry: , the second dimension of the transform.
3: – Complex (Kind=nag_wp) arrayInput
On entry: the Hermitian sequence of complex input dataset , where
is stored in , for and . That is, if y is regarded as a two-dimensional array of dimension , must contain .
4: – Real (Kind=nag_wp) arrayOutput
On exit: the real output dataset , where
is stored in , for and . That is, if x is regarded as a two-dimensional array of dimension , contains .
5: – IntegerInput/Output
On entry: ifail must be set to , or to set behaviour on detection of an error; these values have no effect when no error is detected.
A value of causes the printing of an error message and program execution will be halted; otherwise program execution continues. A value of means that an error message is printed while a value of means that it is not.
If halting is not appropriate, the value or is recommended. If message printing is undesirable, then the value is recommended. Otherwise, the value is recommended. When the value or is used it is essential to test the value of ifail on exit.
On exit: unless the routine detects an error or a warning has been flagged (see Section 6).
6Error Indicators and Warnings
If on entry or , explanatory error messages are output on the current error message unit (as defined by x04aaf).
Errors or warnings detected by the routine:
On entry, .
On entry, .
An internal error has occurred in this routine.
Check the routine call and any array sizes.
If the call is correct then please contact NAG for assistance.
An unexpected error has been triggered by this routine. Please
See Section 7 in the Introduction to the NAG Library FL Interface for further information.
Your licence key may have expired or may not have been installed correctly.
See Section 8 in the Introduction to the NAG Library FL Interface for further information.
Dynamic memory allocation failed.
See Section 9 in the Introduction to the NAG Library FL Interface for further information.
Some indication of accuracy can be obtained by performing a forward transform using c06pvf and a backward transform using c06pwf, and comparing the results with the original sequence (in exact arithmetic they would be identical).
8Parallelism and Performance
Background information to multithreading can be found in the Multithreading documentation.
c06pwf is threaded by NAG for parallel execution in multithreaded implementations of the NAG Library.
c06pwf makes calls to BLAS and/or LAPACK routines, which may be threaded within the vendor library used by this implementation. Consult the documentation for the vendor library for further information.
Please consult the X06 Chapter Introduction for information on how to control and interrogate the OpenMP environment used within this routine. Please also consult the Users' Note for your implementation for any additional implementation-specific information.
The time taken by c06pwf is approximately proportional to , but also depends on the factors of and . c06pwf is fastest if the only prime factors of and are , and , and is particularly slow if or is a large prime, or has large prime factors.
Workspace is internally allocated by c06pwf. The total size of these arrays is approximately proportional to .