Re: octave vs. matlab vectorization

[Francesco Potorti`]

>since i was raised to vectorize loop structures whenever possible, i  
>thought i would illustrate the the speed-up for the students in the  
>class by comparing execution time for two codes--code 1 with loops,  
>and code 2 vectorized.
>
>here is code 1:
>
>t0=clock;
>for m=1:1000000
>       q=zeros(1,10);
>       for k=1:10,
>               tmp=k^2;
>               if tmp>50,
>                       q(k)=tmp;
>               else
>                       q(k)=0;
>               end
>       end
>end
>etime(clock,t0)
>
>here is code 2:
>
>t0=clock;
>for m=1:1000000
>       q=zeros(1,10);
>       tmp=(1:10).^2;
>       q=tmp.*(tmp>50);
>end
>etime(clock,t0)
>
>on my laptop, octave (3.0.5) takes 200 secs for the first code and  
>just 24 secs for the second--i thought i had proved my point.

A ratio of 8.3:1

>however, on the department server (admittedly a much faster machine),  
>matlab ground through the first code in 0.82 secs while the second  
>code took 4.3 secs.

A ratio of 5.2:1.  Not quite the same, but I think the point is proven
nonetheless.

-- 
Francesco Potortì (ricercatore)        Voice: +39 050 315 3058 (op.2111)
ISTI - Area della ricerca CNR          Fax:   +39 050 315 2040
via G. Moruzzi 1, I-56124 Pisa         Email: address@hidden
(entrance 20, 1st floor, room C71)     Web:   http://fly.isti.cnr.it/