[Python-Dev] math.areclose ...?

Aahz aahz at pythoncraft.com
Mon Feb 6 21:20:31 CET 2006

On Mon, Feb 06, 2006, Chris or Leslie Smith wrote:
> || def areclose(x,y,rtol=1.e-5,atol=1.e-8):
> ||      return abs(x-y)<atol+rtol*abs(y)
> | 
> | Looks interesting.  I don't quite understand what atol/rtol are,
> | though. 
> Does it help to spell it like this?
> def areclose(x, y, relative_err = 1.e-5, absolute_err=1.e-8):
>   diff = abs(x - y)
>   ave = (abs(x) + abs(y))/2
>   return diff < absolute_err or diff/ave < relative_err
> Also, separating the two terms with 'or' rather than '+' makes the
> two error terms mean more what they are named. The '+' mixes the two
> effects and even though the result is basically the same, it makes it
> difficult to explain when the test will be true.

Yes, that's a big help.  I was a bit concerned that this would have no
utility for numbers with large magnitude.  Alex, given your focus on
Python readability, I'm a bit surprised you didn't write this to start
Aahz (aahz at pythoncraft.com)           <*>         http://www.pythoncraft.com/

"19. A language that doesn't affect the way you think about programming,
is not worth knowing."  --Alan Perlis

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