polyfit test fails

[Ben Abbott]

On May 21, 2009, at 9:57 AM, Marco Atzeri wrote:

>
> Dear all,
> on latest hg source, on cygwin-1.7, I have
>
>
>>>>>> processing /pub/hg/octave_clone/scripts/polynomial/polyfit.m
>  ***** test
> x = [ -1196.4, -1195.2, -1194, -1192.8, -1191.6, -1190.4, -1189.2,  
> -1188, \
>       -1186.8, -1185.6, -1184.4, -1183.2, -1182];
> y = [ 315571.7086, 315575.9618, 315579.4195, 315582.6206,  
> 315585.4966,    \
>       315588.3172, 315590.9326, 315593.5934, 315596.0455,  
> 315598.4201,    \
>       315600.7143, 315602.9508, 315605.1765 ];
> [p1, s1] = polyfit (x, y, 10);
> [p2, s2, mu] = polyfit (x, y, 10);
> assert (2*s2.normr < s1.normr)
> !!!!! test failed
>
>
>
> octave:5> 2*s2.normr
> ans =  0.12583
> octave:6>  s1.normr
> ans =  0.11466
>
>
> is this fault cygwin specific or do you see it
> on other platform ?

For OSX I get ...

octave:8> x = [ -1196.4, -1195.2, -1194, -1192.8, -1191.6, -1190.4,  
-1189.2, -1188, \
 >       -1186.8, -1185.6, -1184.4, -1183.2, -1182];
octave:9> y = [ 315571.7086, 315575.9618, 315579.4195, 315582.6206,  
315585.4966,    \
 >       315588.3172, 315590.9326, 315593.5934, 315596.0455,  
315598.4201,    \
 >       315600.7143, 315602.9508, 315605.1765 ];
octave:10> [p1, s1] = polyfit (x, y, 10);
octave:11> [p2, s2, mu] = polyfit (x, y, 10);
octave:12> assert (2*s2.normr < s1.normr)
octave:13> 2*s2.normr
ans =  0.12583
octave:14> s1.normr
ans =  0.25320

If I understand these results correctly, it appears  your result is  
better than expected.

Perhaps the test should be changed.

Ben