Comparing floats

[Marco Nawijn]

On 29 nov, 00:20, Nobody <nob... at nowhere.com> wrote:
> On Sat, 27 Nov 2010 18:23:48 -0500, Terry Reedy wrote:
> >> Therefore, to implement this multiplication operation I need to have a
> >> way to verify that the float tuples C and D are "equal".
>
> > I might try the average relative difference:
> > sum(abs((i-j)/(i+j)) for i,j in zip(C,D))/n # assuming lengths constant
>
> The division is unstable if i and j are close to zero.
>
> For scalars, I'd use:
>
>         abs(i-j) <= epsilon * (1 + abs(i+j))
>
> This amounts to a relative error check for large values and an absolute
> error check for values close to zero.
>
> For a vector, I'd check that the above holds for all pairs.

Hi All,

Why don't you treat the C and D tuples as vectors? You can than check
dot product
and norm (length) for equality. Using scipy (www.scipy.org), you even
get very nice
performance.

Marco