[Octave-bug-tracker] [bug #49667] Computing powers of complex numbers in 4.2.0 is slower than in 4.0.3

[Marco Caliari]

URL:
  <http://savannah.gnu.org/bugs/?49667>

                 Summary: Computing powers of complex numbers in 4.2.0 is
slower than in 4.0.3
                 Project: GNU Octave
            Submitted by: caliari
            Submitted on: Tue 22 Nov 2016 09:13:13 AM GMT
                Category: Performance
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Regression
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.2.0
        Operating System: GNU/Linux

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Details:

Dear all,

I compiled from scratch 4.0.3 and 4.2.0 and observe the following


GNU Octave, version 4.2.0
>> z=rand(1000)+1i*rand(1000);
tic,z.*z;,toc,tic,z.^2;,toc,tic,exp(2*log(z));,toc
Elapsed time is 0.0171239 seconds.
Elapsed time is 0.247205 seconds.
Elapsed time is 0.243459 seconds.

GNU Octave, version 4.0.3
>> z=rand(1000)+1i*rand(1000);
tic,z.*z;,toc,tic,z.^2;,toc,tic,exp(2*log(z));,toc
Elapsed time is 0.00733209 seconds.
Elapsed time is 0.017849 seconds.
Elapsed time is 0.245989 seconds.


So, it seems that integer powers of complex numbers are now treated as double
powers. I'm on Mint 17.3 (Ubuntu 14.04). A user in chat showed me that 4.2.0
behaves like 4.0.3 on Ubuntu 16.04. So, it is an Ubuntu 14.04 related problem.




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