Node:Using Plans, Next:Basic Interface, Previous:Data Types and Files, Up:FFTW Reference
Plans for all transform types in FFTW are stored as type
fftw_plan (an opaque pointer type), and are created by one of the
various planning routines described in the following sections.
fftw_plan contains all information necessary to compute the
transform, including the pointers to the input and output arrays.
void fftw_execute(const fftw_plan plan);
This executes the
plan, to compute the corresponding transform on
the arrays for which it was planned (which must still exist). The plan
is not modified, and
fftw_execute can be called as many times as
To apply a given plan to a different array, you can use the guru interface. See Guru Interface.
fftw_execute (and equivalents) is the only function in FFTW
guaranteed to be thread-safe; see Thread safety.
void fftw_destroy_plan(fftw_plan plan);deallocates the
planand all its associated data.
FFTW's planner saves some other persistent data, such as the
accumulated wisdom and a list of algorithms available in the current
configuration. If you want to deallocate all of that and reset FFTW
to the pristine state it was in when you started your program, you can
This does not deallocate your plans; you should still call
fftw_destroy_plan if you want to do this. You should not execute
any previously created plans after calling
The following two routines are provided purely for academic purposes
(that is, for entertainment).
void fftw_flops(const fftw_plan plan, double *add, double *mul, double *fma);
fma to an
exact count of the number of floating-point additions, multiplications,
and fused multiply-add operations involved in the plan's execution. The
total number of floating-point operations (flops) is
add + mul +
add + mul + fma if the hardware supports fused
multiply-add instructions (although the number of FMA operations is only
approximate because of compiler voodoo). (The number of operations
should be an integer, but we use
double to avoid overflowing
int for large transforms; the arguments are of type
even for single and long-double precision versions of FFTW.)
void fftw_fprint_plan(const fftw_plan plan, FILE *output_file); void fftw_print_plan(const fftw_plan plan);
This outputs a "nerd-readable" representation of the
the given file or to