a more precise distance algorithm

[ravas]

On Monday, May 25, 2015 at 10:16:02 PM UTC-7, Gary Herron wrote:
> It's probably not the square root that's causing the inaccuracies. In 
> many other cases, and probably here also, it's the summing of two 
> numbers that have vastly different values that loses precision.  A 
> demonstration:
> 
>  >>> big = 100000000.0
>  >>> small = 0.000000001
>  >>> (big+small)-big # Should produce a value =small, but gives an exact 
> zero instead.
> 0.0
> 
> The squaring of the two values in x*x+y*y just makes the addition even 
> more error prone since the squares make large values even larger and 
> small values even smaller.

I appreciate your help.