z = mat2cell(1:1e6,1,repmat(1,1,1e6));
f = @() cellfun(‘isempty’,z);
g = @() cellfun(@isempty,z);

a1=timeit(f)
a1 =
0.0053
a2=timeit(g)
a2 =
0.7142

a2/a1
ans =
135.1974

>> c = mat2cell(1:1e6,1,repmat(1,1,1e6));
>> tic, d=cellfun('isempty',c); toc
Elapsed time is 0.0282919 seconds.

>> tic, d=cellfun(@isempty,c); toc
Elapsed time is 0.0258329 seconds.

>> 0.0258329 / 0.0282919
ans =  0.91308

>> c = mat2cell(1:1e6,1,repmat(1,1,1e6));
>> tic, d=cellfun('isempty',c); toc
Elapsed time is 0.011489 seconds.

>> tic, d=cellfun(@isempty,c); toc
Elapsed time is 0.927122 seconds.

>> 0.927122/0.011489
ans =
   80.6965

>> c = mat2cell(1:1e6,1,repmat(1,1,1e6));
>> tic, d=cellfun('isempty',c); toc
Elapsed time is 0.008351 seconds.

>> tic, d=cellfun(@isempty,c); toc
Elapsed time is 0.461371 seconds.

>> 0.461371 / 0.008351
ans =
   55.2474

>> c = mat2cell(1:1e6,1,repmat(1,1,1e6));
>> tic, d=cellfun('isempty',c); toc
Elapsed time is 0.011079 seconds.

>> tic, d=cellfun(@isempty,c); toc
Elapsed time is 0.618598 seconds.

The gap is still present

 
>> c = mat2cell(1:1e6,1,repmat(1,1,1e6));
>> tic, d=cellfun('isempty',c); toc
Elapsed time is 0.038423 seconds.

>> tic, d=cellfun(@isempty,c); toc
Elapsed time is 0.681082 seconds.

>> 0.681082/0.038423
ans =
   17.7259

The MathWorks don’t seem to be in a rush to optimize this…

>> c = mat2cell(1:1e6,1,repmat(1,1,1e6));
>> tic, d=cellfun('isempty',c); toc
Elapsed time is 0.032773 seconds.

>> tic, d=cellfun(@isempty,c); toc
Elapsed time is 2.100385 seconds.

>> 2.100385/0.032773
ans =
   64.0889

I looked at your example, and I noticed that in Octave we hadn’t quite optimised this as much as possible. I went ahead and committed a change to fix this:

http://hg.savannah.gnu.org/hgweb/octave/rev/cf8cd43cdeb3

On my laptop with Intel Core 2 Duo @ 2.20G, I see the following:

octave:1> c = mat2cell(1:1e6,1,repmat(1,1,1e6));
octave:2> tic, d=cellfun('isempty',c); toc
Elapsed time is 0.0171831 seconds.
octave:3> tic, d=cellfun('isempty',c); toc
Elapsed time is 0.0182698 seconds.
octave:4> tic, d=cellfun('isempty',c); toc
Elapsed time is 0.0223808 seconds.

octave:5> tic, d=cellfun(@isempty,c); toc
Elapsed time is 0.0193319 seconds.
octave:6> tic, d=cellfun(@isempty,c); toc
Elapsed time is 0.01612 seconds.
octave:7> tic, d=cellfun(@isempty,c); toc
Elapsed time is 0.019449 seconds.

This should be part of our 3.6 release that should happen very soon!

Sadly, your preferred method of calling cellfun cannot be easily optimised:

octave:8> tic, d=cellfun(@(x) isempty(x),c); toc
Elapsed time is 0.924903 seconds.
octave:9> tic, d=cellfun(@(x) isempty(x),c); toc
Elapsed time is 0.873197 seconds.
octave:10> tic, d=cellfun(@(x) isempty(x),c); toc
Elapsed time is 0.875425 seconds.

Note that Octave still is single-threaded, so this does not benefit from any parallelisation right now. There’s work to build parallelisation into Octave, so perhaps we can see more dramatic speedups in the future.

@Jordi – thanks. If you have any other comparisons to Octave for any of the other articles here, please do post a comment.