From: Douglas Seifert <doug@...>
Date: 2009-11-22T23:42:34+09:00
Subject: Re: really crazy about this (do/while)

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>
> So my compromise is, when I want to work with some fraction of a number,
> and I
> want it to be as precise as possible (with no regard for performance), I
> make
> it a Rational as long as I can get away with. I can always call to_f on the
> end result.
>
> I might be Doing It Wrong, though. Maybe BigDecimal is the way to go?
>
>
BigDecimal is probably easier to code with, but can kill performance as has
been mentioned previously.  Recalling the old Fortran days, we always had a
constant called EPS we used in these kind of situations.  EPS (short for
epsilon) was set to a small number, usually 1e-7.  Anytime we needed to
compare two floating point values, we would not compare them directly, but
rather compare the absolute value of their difference to EPS.

In the original poster's code, here is how we would have dealt with the
issue:

eps = 1e-7
temp = 98.3
i = 0

begin
 i += 1
 puts "step" + i.to_s + " befre adding is " + temp.to_s
 temp += 0.1
 puts "step" + i.to_s + " after adding is " + temp.to_s
 puts "temp - 98.6: #{temp-98.6}"
 puts
#end while temp < 98.6
end while (temp - 98.6) < -eps

Having to remember to do this all the time is difficult and annoying.

-Doug Seifert

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