Re: PSPP-BUG: moments_calculate error

[Ben Pfaff]

John Darrington <address@hidden> writes:

> I had a look at this one.
>
> The pertinent assertion is:
>
>      /* After the second pass we can calculate any stat.  We
>          don't support "online" computation during the second
>          pass, so As a simple self-check, the total weight for
>          the passes must agree. */
>       assert (m->w1 == m->w2);
>
> and when I ran it through gdb, I see:
>
> Breakpoint 1, moments_calculate (m=0x81430c0, weight=0xbffff1c0, 
> mean=0xbffff1b8, variance=0xbffff1b0, skewness=0xbffff1a8, 
>     kurtosis=0xbffff1a0) at /home/john/pspp-master/src/math/moments.c:233
> 233           assert (m->w1 == m->w2);
> (gdb) print m
> $2 = {max_moment = MOMENT_KURTOSIS, pass = 2, w1 = 2257.1583655975705, sum = 
> 970999467.71251988, mean = 430186.6818527166, 
>   w2 = 2257.1583655975778, d1 = 6.8955123424530029e-06, d2 = 
> 1504554313897766, d3 = 2.7440683550398496e+21, 
>   d4 = 9.0176522508330139e+27}
>
> So it would appear that this is simply a floating point
> precision problem (which inevitably arises when doing equality
> comparisons with floating points).  So I suggest that this
> assertion be deleted.

w1 and w2 are each calculated as the sum of the same sequence of
values in the same order.  It's not obvious the results could
differ, even slightly, without the sequences also differing in
some way.