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fftw_flags

set method for fft planner algorithm selection

Syntax

[a,[S]]=fftw_flags(flag)

Arguments

flag

a string or an integer. Specifies the planner algorithm. See below.

a

an integer. The planner code. See below.

S

a character string. The planner name.

Description

This function enables the selection of the algorithm used to determine the fftw planner algorithm. The planner is used to determine an efficient way to compute the fft.

Warning: the default value "FFTW_ESTIMATE" gives generally quite efficient plans. Try to change it only if the fft efficiency is really important and you have a lot of similar calls to do.

Accepted entries are :

Remark : when using FFTW_MEASURE/FFTW_PATIENT/FFTW_EXHAUSTIVE you must call fftw twice. (first call for initialization, second and others calls for computation)

Examples

A=rand(1, 2^9 + 2^15);
fftw_forget_wisdom();
fftw_flags("FFTW_ESTIMATE");
timer(); y=fft(A); timer()//first call determines the plan
timer(); y=fft(A); timer() //subsequent similar calls
fftw_flags("FFTW_MEASURE");
fftw_forget_wisdom();
timer(); y=fft(A); timer()//first call determines the plan, this takes about 5min
timer(); y=fft(A); timer() //subsequent similar calls

See also


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