RE: [PHP] Math Weirdness

On 15 July 2008 14:33, tedd advised:

> At 11:24 AM +0100 7/15/08, Ford, Mike wrote:
>> On 14 July 2008 20:47, tedd advised:
>>
>> > Round-off errors normally don't enter into things unless your
doing
>> > multiplication and division operations. At that point,
> what you get
>>> back from the operation is an approximation and not the actual
>>> number.
>>
>> Bull! Nearly all computer floating point numbers are approximations
>> because of being held in binary rather than decimal. Any number with
a
>> (decimal) fractional part that doesn't end with the digit 5 is
>> necessarily an approximation, and that's only half the story. So as
soon
>> as you involve numbers like 0.1 or 0.2, you've already got minor
>> inaccuracies which will propagate through any kind of arithmetic --
it's
>> just worse with multiplication or division because these tend to
result
>> in inaccuracy in more significant digits!
>>
>> Bottom line: a floating point value should *always* be treated with
an
>> appropriate degree of suspicion.
>>
>> Cheers!
>>
>> Mike
>
> Mike:
>
> No reason to be rude.
>
> I said:
>
> "Round-off errors normally don't enter into things unless your doing
> multiplication and division operations."
>
> And that is not "Bull" -- it's true. You can add and subtract all the
> floating point numbers (the one's we are talking about here) you want
> without any rounding errors whatsoever.

Sorry, I do apologise if I came over too strongly -- there was no
intention to offend.

However, you really can't dismiss the effects of round-off errors on
addition and subtraction as lightly as that. It's simply not true that
approximations only occur at the point of doing multiplication and
division -- there *are* approximations involved in addition and
subtraction, and it is necessary to be aware that this is the case -- as
Jay proved, 0.1+0.2 is hardly ever exactly 0.3. In this sort of case, it
may well be that an appropriate degree of suspicion is simply to round
to 2 decimal places at every stage, or compare the absolute difference
to .001, but nonetheless one has to *know* that this is necessary.

Ummm -- sorry, better </rant>, now!!!

Cheers!

Mike

--
Mike Ford, Electronic Information Developer,
C507, Leeds Metropolitan University, Civic Quarter Campus,
Woodhouse Lane, LEEDS, LS1 3HE, United Kingdom
Email: m.ford@leedsmet.ac.uk
Tel: +44 113 812 4730


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Robert Cummings schreef:
> On Tue, 2008-07-15 at 12:37 -0400, tedd wrote:
>> At 12:31 PM -0400 7/15/08, Robert Cummings wrote:
>>> Umm... here it is to unlimited precision: ¼
>>>
>>> Cheers,
>>> Rob.
>> Yeah and here's Æ’
>>
>> Like or not, that's all there is to it.
>
> Weird... you're client bastar-dized my beautiful pi symbol.

no it's the worst round error ever. how exactly do you go
from 3.1 to .25 :-P

>
> Cheers,
> Rob.

[snip]
Ask Jay, he's the skimming master! >:)
[/snip]

Bow down before me....but not too far lest ye be skimmed as well.

Jochem Maas wrote:
> Robert Cummings schreef:
>> On Tue, 2008-07-15 at 12:37 -0400, tedd wrote:
>>> At 12:31 PM -0400 7/15/08, Robert Cummings wrote:
>>>> Umm... here it is to unlimited precision: ¼
>>>>
>>>> Cheers,
>>>> Rob.
>>> Yeah and here's Æ’
>>>
>>> Like or not, that's all there is to it.
>>
>> Weird... you're client bastar-dized my beautiful pi symbol.
>
> no it's the worst round error ever. how exactly do you go
> from 3.1 to .25 :-P

Easy, subtract 2.85

-Shawn

>
>>
>> Cheers,
>> Rob.
>

On Jul 16, 2008, at 11:39 AM, Shawn McKenzie wrote:

> Jochem Maas wrote:
>> Robert Cummings schreef:
>>> On Tue, 2008-07-15 at 12:37 -0400, tedd wrote:
>>>> At 12:31 PM -0400 7/15/08, Robert Cummings wrote:
>>>>> Umm... here it is to unlimited precision: ¼
>>>>>
>>>>> Cheers,
>>>>> Rob.
>>>> Yeah and here's ƒ
>>>>
>>>> Like or not, that's all there is to it.
>>>
>>> Weird... you're client bastar-dized my beautiful pi symbol.
>> no it's the worst round error ever. how exactly do you go
>> from 3.1 to .25 :-P
>
> Easy, subtract 2.85

And then put it in Jay's pocket since we know he's skimming! If you're
lucky maybe he'll cut you in for not telling the boss :P


--

Jason Pruim
Raoset Inc.
Technology Manager
MQC Specialist
11287 James St
Holland, MI 49424
www.raoset.com
japruim@raoset.com

[snip]
And then put it in Jay's pocket since we know he's skimming! If you're
lucky maybe he'll cut you in for not telling the boss :P
[/snip]

"Allegedly".

On Tue, Jul 15, 2008 at 3:50 PM, tedd <tedd.sperling@gmail.com> wrote:
>
> Well, someone's client took infinity and turned it into an integral.
>
> tdd

Yeah, but they stole your 'e' to make up for it.

--
</Daniel P. Brown>
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