Re: isreal benchmarking

[Rik]

On 09/10/2012 04:02 PM, Daniel J Sebald wrote:
>> Incidentally, I did a little benchmarking and automatic narrowing is ~25%
>> faster than using an equivalent vectorized operator.
>>
>> Example code:
>> x = complex (ones (1e4), zeros (1e4));
>>
>> tic; xreal = isreal ([x]); toc
>> Elapsed time is 1.78048 seconds.
>>
>> tic; xreal = all (imag (x) == 0); toc
>> Elapsed time is 2.42 seconds.
>
> That's not what I'm getting...
>
> octave:1> x = complex (ones (1e4), zeros (1e4));
> octave:2>
> octave:2> cpustart = cputime();
> octave:3> xisreal = isreal(x)
> xisreal = 0
> octave:4> cputime() - cpustart
> ans =  0.0029990
> octave:5>
> octave:5> cpustart = cputime();
> octave:6> xisreal = isreal([x])
> xisreal =  1
> octave:7> cputime() - cpustart
> ans =  1.5658
> octave:8>
> octave:8> cpustart = cputime();
> octave:9> xisreal = isreal(x(:))
> xisreal =  1
> octave:10> cputime() - cpustart
> ans =  1.5678
> octave:11>
> octave:11> cpustart = cputime();
> octave:12> xisreal = all (all (imag (x) == 0))
> xisreal =  1
> octave:13> cputime() - cpustart
> ans =  1.4528
>
> What brand of computer do you have there Rik?
Hmm.  It's not that bad.  I'm using a mainstream Intel Core2 Duo.

Benchmarking though can be tricky.  Did you disable frequency scaling for
your CPU?  If not, the first tests impose a load on the CPU which then
responds by increasing its operating frequency and later tests run faster. 
There wasn't a sudden change in system load during the test was there such
as a cron job coming to life?

I just re-benchmarked using your exact code and I still get the result that
narrowing is faster.  This is on a development build from about a week ago.

--Rik