[samigo-team] Floating point numbers

[Karen Tsao]

Thanks, Sam. I will take a good.

Karen

On Sun, Mar 10, 2013 at 10:31 AM, Sam Ottenhoff <ottenhoff at longsight.com>wrote:

> Okay, I attached a patch to https://jira.sakaiproject.org/browse/SAM-2087.
>
> I also have a demo server up: http://198.30.168.81:15150/portal/.  Sakai
> demo mode is enabled so you can login with a username like
> instructor1/sakai or student0012/sakai.
>
> All of my tests look good so far.  This change makes sense to me.  The
> gradebook uses double-precision numbers for recording points.  Samigo
> should do the same thing.
>
> This is a large change.  It essentially changes all occurrences of floats
> with doubles.
>
> --Sam
>
>
> On Tue, Mar 5, 2013 at 11:34 AM, Sam Ottenhoff <ottenhoff at longsight.com>wrote:
>
>> I gave it a try, but it involves 1000+ changes.  It probably makes sense
>> to just improve precision and move from floats to doubles instead.  The
>> gradebook records POINTS_EARNED as a double.
>>
>>
>> On Thu, Feb 28, 2013 at 2:16 PM, Karen Tsao <ktsao at stanford.edu> wrote:
>>
>>> Thanks for everyone's input.
>>>
>>> Sam,
>>>
>>> Could you please make the change? Thanks!
>>>
>>> Karen
>>>
>>>
>>> On Thu, Feb 28, 2013 at 6:19 AM, David Horwitz <david.horwitz at uct.ac.za>wrote:
>>>
>>>>  There's a another issue (fixable without replacing floats but still)
>>>>
>>>> There are several places in the code where direct foat comparisons are
>>>> made:
>>>>
>>>> Float a =
>>>> Float b,
>>>>
>>>> if (a.equals(b))
>>>>
>>>> For instance to check if an answer has been updated etc. We could be
>>>> getting extra updated because of slight differences in the float
>>>> representation ...
>>>>
>>>> D
>>>>
>>>>
>>>> On Thu, 2013-02-28 at 09:11 -0500, Sam Ottenhoff wrote:
>>>>
>>>>
>>>>  But just curious, what is the advantage of this change? Is this for
>>>> getting a more precise score? Like some 0.999 issue?
>>>>
>>>>
>>>>
>>>>  An instructor created a complex placement exam that used point scores
>>>> in the millions, thousands, hundreds, etc. as a way of being able to
>>>> quickly see points in various sections in the final score (example:
>>>> 27005508.06 could be broken up to see that the student scores 06 on sec 1,
>>>> 08, on sec 2, 55 on sec 3, 27 on sec 4).
>>>>
>>>>
>>>>
>>>>  So the reason why floating point numbers aren't used for money:
>>>>
>>>>
>>>>
>>>>  > create table floattest (z float);
>>>>
>>>> > insert into floattest VALUES (*2075808*);
>>>>
>>>> > select * from floattest;
>>>>
>>>>
>>>>
>>>>  The result: *2075810*
>>>>
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>>>>
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>>
>
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