Chris@19: Next: Caveats in Using Wisdom, Chris@19: Previous: Multi-dimensional Array Format, Chris@19: Up: Other Important Topics Chris@19:
Chris@19: FFTW implements a method for saving plans to disk and restoring them. Chris@19: In fact, what FFTW does is more general than just saving and loading Chris@19: plans. The mechanism is called wisdom. Here, we describe Chris@19: this feature at a high level. See FFTW Reference, for a less casual Chris@19: but more complete discussion of how to use wisdom in FFTW. Chris@19: Chris@19:
Plans created with the FFTW_MEASURE, FFTW_PATIENT, or
Chris@19: FFTW_EXHAUSTIVE options produce near-optimal FFT performance,
Chris@19: but may require a long time to compute because FFTW must measure the
Chris@19: runtime of many possible plans and select the best one. This setup is
Chris@19: designed for the situations where so many transforms of the same size
Chris@19: must be computed that the start-up time is irrelevant. For short
Chris@19: initialization times, but slower transforms, we have provided
Chris@19: FFTW_ESTIMATE. The wisdom mechanism is a way to get the
Chris@19: best of both worlds: you compute a good plan once, save it to
Chris@19: disk, and later reload it as many times as necessary. The wisdom
Chris@19: mechanism can actually save and reload many plans at once, not just
Chris@19: one.
Chris@19:
Chris@19:
Chris@19:
Whenever you create a plan, the FFTW planner accumulates wisdom, which Chris@19: is information sufficient to reconstruct the plan. After planning, Chris@19: you can save this information to disk by means of the function: Chris@19:
int fftw_export_wisdom_to_filename(const char *filename); Chris@19:Chris@19:
(This function returns non-zero on success.) Chris@19: Chris@19:
The next time you run the program, you can restore the wisdom with
Chris@19: fftw_import_wisdom_from_filename (which also returns non-zero on success),
Chris@19: and then recreate the plan using the same flags as before.
Chris@19:
int fftw_import_wisdom_from_filename(const char *filename); Chris@19:Chris@19:
Chris@19: Wisdom is automatically used for any size to which it is applicable, as
Chris@19: long as the planner flags are not more “patient” than those with which
Chris@19: the wisdom was created. For example, wisdom created with
Chris@19: FFTW_MEASURE can be used if you later plan with
Chris@19: FFTW_ESTIMATE or FFTW_MEASURE, but not with
Chris@19: FFTW_PATIENT.
Chris@19:
Chris@19:
The wisdom is cumulative, and is stored in a global, private
Chris@19: data structure managed internally by FFTW. The storage space required
Chris@19: is minimal, proportional to the logarithm of the sizes the wisdom was
Chris@19: generated from. If memory usage is a concern, however, the wisdom can
Chris@19: be forgotten and its associated memory freed by calling:
Chris@19:
void fftw_forget_wisdom(void); Chris@19:Chris@19:
Chris@19: Wisdom can be exported to a file, a string, or any other medium. Chris@19: For details, see Wisdom. Chris@19: Chris@19: Chris@19: