Re: Comparing Floating Point Values

["Adam Beneschan" <adam@irvine.com>]

markp wrote:
> I was wondering if there was a convention for comparing 2 floats
> dealing with significant digits. For example, if I had 2 variables (x
> and y) and wanted to see if they were equal in an if statement, is
> there a standard way to do a compare based on "x" significant digits?
>
> Thank you.

I don't do a lot of floating-point programming, so I don't know whether
there's a standard.  I would do something like

   if abs(x-y) <= epsilon * x then --- treat x and y as equal...

where epsilon is some suitable small constant or named number.  But
this really isn't my area of knowledge, and if someone else has a
different idea you should trust theirs rather than mine.  And I
wouldn't call this a "convention", which implies that this is sort of
like a "custom" that everyone agrees to follow; the correct value of
epsilon, and the correct way to compare, really depend on a
mathematical analysis of your particular problem.

                           -- Adam