[Numpy-discussion] Different results from repeated calculation

[Stefan van der Walt]

On Sat, Jan 27, 2007 at 04:11:59PM -0700, Fernando Perez wrote:
> OK, this is weird.  I modified the repeat code a little to ease
> collecting of results, and all of a sudden the differences went away.
> If you look at the attached code, here's what happens for me:
> 
> a) If I have line 77 like this (commented out):
> 
>    #print '-'*75
> 
> I get:
> 
> [...]
> 94 z different 8.47032947254e-22
> 95 z different 8.47032947254e-22
> 96 z different 8.47032947254e-22
> 98 z different 8.47032947254e-22
> 99 z different 8.47032947254e-22
> 
> Numpy version: 1.0.2.dev3521
> 
> test1:  0  differences
> test2:  75  differences
> test3:  0  differences
> 
> 
> 
> b) If I remove the comment char from that line, I get:
> 
> tlon[~/Desktop]> python repeat.py
> 
> ---------------------------------------------------------------------------
> Numpy version: 1.0.2.dev3521
> 
> test1:  0  differences
> test2:  0  differences
> test3:  0  differences
> 
> 
> That's it.  One comment char removed, and something that's done
> /after/ the tests are actually executed.
> 
> That kind of 'I add a printf() call and the bug disappears' is
> unpleasantly reminiscent of lurking pointer errors in C code...

I also ran the test under Valgrind, but no errors pop up.  Very strange.

Cheers
Stéfan