On 2010-03-16 17:55 PM, JLundell wrote:
On Mar 16, 8:06 am, Robert Kern<robert.k...@gmail.com> wrote:
On 2010-03-16 07:35 AM, Dave Angel wrote:
Carl Banks wrote:
On Mar 15, 4:34 pm, JLundell<jlund...@pobox.com> wrote:
It's also unfortunate that Python doesn't have an approximately-equal
operator; it'd come in handy for floating-point applications while
preserving hash. If only there were a ~=r ≈ operator I could
overload. And ~ is unary, so no joy.
One problem with it is that there's no way to make it universal;
different appiplications have different ideas of close. Conceivably
it could be usefully defined for a user type though..
Bacause of this problem almost no languages have an almost equal
operator. I'm curious what languages do, of if there are any with a
trinary operator that also takes a threshold.
Carl Banks
If I recall correctly, APL has a *fuzz* value, which is used in all(?)
comparisons. But I do not recall anything about how it was defined. I do
recall that you could change the threshold, and suspect it was relative
to the operands. For symmetry, it would probably have to be relative to
the average of the two values, or some such.
The problem is that frequently there is no system-wide fuzz value which is
appropriate for all comparisons in a given program. You need to choose the right
value for each comparison. Consequently, you might as well use a function
instead of an operator and a global variable.
--
Robert Kern
APL scaled their fuzz to the larger of the values being compared.
I know. My statement stands for relative fuzz values as well as it does for
absolute fuzz values. :-)
In
my case, my domain permits me to use a constant fuzz; all my units are
the same (votes, as it happens). I've seen abs(a/b-1) used instead of
abs(a-b); obviously you'd need to treat comparison with zero
specially.
One usually uses a combination of relative and absolute tolerances to account
for the case when the values are close to zero.
But yeah, it's really a domain-specific problem.
Right. And a single program might need to deal with multiple domains, so a
single global setting to control a language feature is pretty fragile.
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
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