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Re: tic toc


From: John Reed
Subject: Re: tic toc
Date: Tue, 05 Jan 2010 09:25:31 -0800

Hi John,

Thank you for the explanation.  Since Octave is making system calls to get the 
timing info it sounds like any bugs would be elsewhere in my system rather than 
within Octave.     

Some system information: 

running on XP service pack 2

it has intel core 2 duo processors (2.2 GHz)

and it uses visual C++ 2005.

Should I still report this issue to address@hidden even though the bug appears 
to be in Windows?  If it would be useful I will go ahead and report it.

Thanks,

John

>>> "John W. Eaton" <address@hidden> 1/4/2010 11:23 PM >>>
On  4-Jan-2010, John Reed wrote:

| Hello,
| 
| I've been getting some strange results using tic toc and cputime to get wall 
time and cputime for an operation using the find() function.
| 
| for example:
| 
| tic;
| c=cputime();
| 
|  ind = find( T(:,1) >= -121.9 & ...
|                           T(:,1) < -121.8 & ...         
|                           T(:,2) >= 37 & ...
|                          T_coord_search(:,2) < 37.1 );
|  
| 
| t=toc;
| 
| c=cputime() - c;
| 
| fprintf("wall time was %e seconds \n",t);
| 
| fprintf("cputime was %e seconds \n",c);
| 
| Where T is a 409981 x 2 array of doubles.
| 
| sometimes the script returns about 0.016 seconds for both times which seems 
reasonable for this operation
| 
| on other occasions  for the exact same array and conditions the script 
returns a wall time of ~ 1e-8 seconds and cputime of 0 seconds which seems 
unreasonable (sometimes the wall time is even given as a negative number)
| 
| Am I using tic toc and cputime incorrectly?

It looks like you are.

|  Or is the time for find to operate really this widely variable?  Or could 
something be happening peculiar to my system that is causing tic and toc and 
cputime to malfunction?

I would not expect negative values for wall clock or CPU time.

It's possible that you've found a bug in Octave, but Octave
is just making system calls to get the values and then returning them
to you, so it seems more likely that those functions are

| Any thoughts or advice someone might have would be greatly appreciated.

What kind of system do you have?  Does it have multiple CPUs?  What
operating system and version are you using?  What C library and
version?  etc.

If you think you've found a bug in Octave, then please submit a
complete bug report to the address@hidden list.

Please read http://www.octave.org/bugs.html to see what kind of
information to include so that someone might be able to reproduce and
debug the problem.

jwe
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