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Chris@42:FFTW implements a method for saving plans to disk and restoring them. Chris@42: In fact, what FFTW does is more general than just saving and loading Chris@42: plans. The mechanism is called wisdom. Here, we describe Chris@42: this feature at a high level. See FFTW Reference, for a less casual Chris@42: but more complete discussion of how to use wisdom in FFTW. Chris@42:
Chris@42:Plans created with the FFTW_MEASURE, FFTW_PATIENT, or
Chris@42: FFTW_EXHAUSTIVE options produce near-optimal FFT performance,
Chris@42: but may require a long time to compute because FFTW must measure the
Chris@42: runtime of many possible plans and select the best one. This setup is
Chris@42: designed for the situations where so many transforms of the same size
Chris@42: must be computed that the start-up time is irrelevant. For short
Chris@42: initialization times, but slower transforms, we have provided
Chris@42: FFTW_ESTIMATE. The wisdom mechanism is a way to get the
Chris@42: best of both worlds: you compute a good plan once, save it to
Chris@42: disk, and later reload it as many times as necessary. The wisdom
Chris@42: mechanism can actually save and reload many plans at once, not just
Chris@42: one.
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Whenever you create a plan, the FFTW planner accumulates wisdom, which Chris@42: is information sufficient to reconstruct the plan. After planning, Chris@42: you can save this information to disk by means of the function: Chris@42:
int fftw_export_wisdom_to_filename(const char *filename); Chris@42:
(This function returns non-zero on success.) Chris@42:
Chris@42:The next time you run the program, you can restore the wisdom with
Chris@42: fftw_import_wisdom_from_filename (which also returns non-zero on success),
Chris@42: and then recreate the plan using the same flags as before.
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int fftw_import_wisdom_from_filename(const char *filename); Chris@42:
Wisdom is automatically used for any size to which it is applicable, as
Chris@42: long as the planner flags are not more “patient” than those with which
Chris@42: the wisdom was created. For example, wisdom created with
Chris@42: FFTW_MEASURE can be used if you later plan with
Chris@42: FFTW_ESTIMATE or FFTW_MEASURE, but not with
Chris@42: FFTW_PATIENT.
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The wisdom is cumulative, and is stored in a global, private
Chris@42: data structure managed internally by FFTW. The storage space required
Chris@42: is minimal, proportional to the logarithm of the sizes the wisdom was
Chris@42: generated from. If memory usage is a concern, however, the wisdom can
Chris@42: be forgotten and its associated memory freed by calling:
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void fftw_forget_wisdom(void); Chris@42:
Wisdom can be exported to a file, a string, or any other medium. Chris@42: For details, see Wisdom. Chris@42:
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