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## FFT slow in 2.9?

**From**: |
Matthias Brennwald |

**Subject**: |
FFT slow in 2.9? |

**Date**: |
Sun, 4 Feb 2007 19:38:04 +0100 |

Dear all,

`on my Mac (PowerBook G4), fft seems to be about four times slower in
``Octave 2.9.9 (binary from HPC) than in Octave 2.1.71 (binary from
``Fink). Also, 2.9.9 does not seem to use fft-wisdom (the same fft
``would be faster after the first run):
`
on 2.9.9:
octave:1> x=rand(1,2^20); tic; fft(x); toc
Elapsed time is 1.985802 seconds.
octave:2> x=rand(1,2^20); tic; fft(x); toc
Elapsed time is 1.803986 seconds.
octave:3> x=rand(1,2^20); tic; fft(x); toc
Elapsed time is 1.811325 seconds.
octave:4> x=rand(1,2^20); tic; fft(x); toc
Elapsed time is 2.165604 seconds.
on 2.1.71:
octave:1> x=rand(1,2^20); tic; fft(x); toc
ans = 0.76503
octave:2> x=rand(1,2^20); tic; fft(x); toc
ans = 0.50110
octave:3> x=rand(1,2^20); tic; fft(x); toc
ans = 0.50244
octave:4> x=rand(1,2^20); tic; fft(x); toc
ans = 0.49133
and on Matlab 7.1:
>> x=rand(1,2^20); tic; fft(x); toc
Elapsed time is 0.751125 seconds.
>> x=rand(1,2^20); tic; fft(x); toc
Elapsed time is 0.492581 seconds.
>> x=rand(1,2^20); tic; fft(x); toc
Elapsed time is 0.473516 seconds.
>> x=rand(1,2^20); tic; fft(x); toc
Elapsed time is 0.486890 seconds.
Any ideas why this is?
Matthias
-------
Matthias Brennwald
Lägernstrasse 6
CH 8037 Zürich
+41 (0)44 364 17 03
address@hidden

**FFT slow in 2.9?**,
*Matthias Brennwald* **<=**