Chris@10: Next: Basic Interface, Chris@10: Previous: Data Types and Files, Chris@10: Up: FFTW Reference Chris@10:
Plans for all transform types in FFTW are stored as type
Chris@10: fftw_plan (an opaque pointer type), and are created by one of the
Chris@10: various planning routines described in the following sections.
Chris@10: An fftw_plan contains all information necessary to compute the
Chris@10: transform, including the pointers to the input and output arrays.
Chris@10:
Chris@10:
void fftw_execute(const fftw_plan plan); Chris@10:Chris@10:
Chris@10: This executes the plan, to compute the corresponding transform on
Chris@10: the arrays for which it was planned (which must still exist). The plan
Chris@10: is not modified, and fftw_execute can be called as many times as
Chris@10: desired.
Chris@10:
Chris@10:
To apply a given plan to a different array, you can use the new-array execute Chris@10: interface. See New-array Execute Functions. Chris@10: Chris@10:
fftw_execute (and equivalents) is the only function in FFTW
Chris@10: guaranteed to be thread-safe; see Thread safety.
Chris@10:
Chris@10:
This function: Chris@10:
void fftw_destroy_plan(fftw_plan plan); Chris@10:Chris@10:
deallocates the plan and all its associated data.
Chris@10:
Chris@10:
FFTW's planner saves some other persistent data, such as the Chris@10: accumulated wisdom and a list of algorithms available in the current Chris@10: configuration. If you want to deallocate all of that and reset FFTW Chris@10: to the pristine state it was in when you started your program, you can Chris@10: call: Chris@10: Chris@10:
void fftw_cleanup(void); Chris@10:Chris@10:
Chris@10: After calling fftw_cleanup, all existing plans become undefined,
Chris@10: and you should not attempt to execute them nor to destroy them. You can
Chris@10: however create and execute/destroy new plans, in which case FFTW starts
Chris@10: accumulating wisdom information again.
Chris@10:
Chris@10:
fftw_cleanup does not deallocate your plans, however. To prevent
Chris@10: memory leaks, you must still call fftw_destroy_plan before
Chris@10: executing fftw_cleanup.
Chris@10:
Chris@10:
Occasionally, it may useful to know FFTW's internal “cost” metric
Chris@10: that it uses to compare plans to one another; this cost is
Chris@10: proportional to an execution time of the plan, in undocumented units,
Chris@10: if the plan was created with the FFTW_MEASURE or other
Chris@10: timing-based options, or alternatively is a heuristic cost function
Chris@10: for FFTW_ESTIMATE plans. (The cost values of measured and
Chris@10: estimated plans are not comparable, being in different units. Also,
Chris@10: costs from different FFTW versions or the same version compiled
Chris@10: differently may not be in the same units. Plans created from wisdom
Chris@10: have a cost of 0 since no timing measurement is performed for them.
Chris@10: Finally, certain problems for which only one top-level algorithm was
Chris@10: possible may have required no measurements of the cost of the whole
Chris@10: plan, in which case fftw_cost will also return 0.) The cost
Chris@10: metric for a given plan is returned by:
Chris@10:
Chris@10:
double fftw_cost(const fftw_plan plan); Chris@10:Chris@10:
Chris@10: The following two routines are provided purely for academic purposes Chris@10: (that is, for entertainment). Chris@10: Chris@10:
void fftw_flops(const fftw_plan plan, Chris@10: double *add, double *mul, double *fma); Chris@10:Chris@10:
Chris@10: Given a plan, set add, mul, and fma to an
Chris@10: exact count of the number of floating-point additions, multiplications,
Chris@10: and fused multiply-add operations involved in the plan's execution. The
Chris@10: total number of floating-point operations (flops) is add + mul +
Chris@10: 2*fma, or add + mul + fma if the hardware supports fused
Chris@10: multiply-add instructions (although the number of FMA operations is only
Chris@10: approximate because of compiler voodoo). (The number of operations
Chris@10: should be an integer, but we use double to avoid overflowing
Chris@10: int for large transforms; the arguments are of type double
Chris@10: even for single and long-double precision versions of FFTW.)
Chris@10:
Chris@10:
void fftw_fprint_plan(const fftw_plan plan, FILE *output_file); Chris@10: void fftw_print_plan(const fftw_plan plan); Chris@10:Chris@10:
Chris@10: This outputs a “nerd-readable” representation of the plan to
Chris@10: the given file or to stdout, respectively.
Chris@10:
Chris@10:
Chris@10:
Chris@10: