Re: [Wikidata] Big numbers

[John Erling Blad]

In the DecimalMath class you escalate scaling on length of fractional part
during multiply. That is what they do in school, but it leads to false
precision. It can be argued that this is both wrong and right. Is there any
particular reason (use case) why you do that? I don't escalate scaling in
the Lua lib.

I see you have bumped into the problem whether precision is a last
digit resolution or a count of significant digits. There are a couple of
(several!) different definitions, and I'm not sure which one is right. 3 ±
0.5 meter is comparable to 120 ±10 inches, but interpretation of "3 meter"
as having a default precision of ±0.5 meter is problematic. It is easier to
see the problem if you compare with a prefix. What is the precision of 3000
meter vs 3 km? And when do you count significant digits? Is zero (0) a
significant digit?

Otherwise I find this extremely amusing. When I first mentioned this we got
into a fierce discussion, and the conclusion was that we should definitely
not use big numbers. Now we do. :D

On Mon, Oct 7, 2019 at 10:44 AM Daniel Kinzler 
wrote:

> Am 07.10.19 um 09:50 schrieb John Erling Blad:
> > Found a few references to bcmath, but some weirdness made me wonder if
> it really
> > was bcmath after all. I wonder if the weirdness is the juggling with
> double when
> > bcmath is missing.
>
> I haven't looked at the code in five years or so, but when I wrote it,
> Number
> was indeed bcmath with fallback to float. The limit of 127 characters
> sounds
> right, though I'm not sure without looking at the code.
>
> Quantity is based on Number, with quite a bit of added complexity for
> converting
> between units while considering the value's precision. e.g. "3 meters"
> should
> not turn into "118,11 inch", but "118 inch" or even "120 inch", if it's the
> default +/- 0.5 meter = 19,685 inch, which means the last digit is
> insignificant. Had lots of fun and confusion with that. I also implemented
> rounding on decimal strings for that. And initially screwed up some edge
> cases,
> which I only realized when helping my daughter with her homework ;)
>
> --
> Daniel Kinzler
> Principal Software Engineer, Core Platform
> Wikimedia Foundation
>
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Re: [Wikidata] Big numbers

[Daniel Kinzler]

Am 07.10.19 um 09:50 schrieb John Erling Blad:
> Found a few references to bcmath, but some weirdness made me wonder if it 
> really
> was bcmath after all. I wonder if the weirdness is the juggling with double 
> when
> bcmath is missing.

I haven't looked at the code in five years or so, but when I wrote it, Number
was indeed bcmath with fallback to float. The limit of 127 characters sounds
right, though I'm not sure without looking at the code.

Quantity is based on Number, with quite a bit of added complexity for converting
between units while considering the value's precision. e.g. "3 meters" should
not turn into "118,11 inch", but "118 inch" or even "120 inch", if it's the
default +/- 0.5 meter = 19,685 inch, which means the last digit is
insignificant. Had lots of fun and confusion with that. I also implemented
rounding on decimal strings for that. And initially screwed up some edge cases,
which I only realized when helping my daughter with her homework ;)

-- 
Daniel Kinzler
Principal Software Engineer, Core Platform
Wikimedia Foundation

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Re: [Wikidata] Big numbers

[John Erling Blad]

Found a few references to bcmath, but some weirdness made me wonder if it
really was bcmath after all. I wonder if the weirdness is the juggling with
double when bcmath is missing.



On Mon, Oct 7, 2019 at 9:18 AM Jeroen De Dauw 
wrote:

> Hey John,
>
> I'm not aware of any documentation, though there probably is some
> somewhere. What I can point you to is the code dealing with numbers:
> https://github.com/wmde/Number
>
> Cheers
>
> --
> Jeroen De Dauw | www.EntropyWins.wtf  |
> www.Professional.Wiki 
> Entrepreneur | Software Crafter | Speaker | Open Souce and Wikimedia
> contributor
> ~=[,,_,,]:3
>
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Re: [Wikidata] Big numbers

[John Erling Blad]

I'm not sure, I have not tried to figure out why, but some places it seems
like the limit hits around 95 chars.

On Mon, Oct 7, 2019 at 9:17 AM Nicolas VIGNERON 
wrote:

> Hi,
>
> The offical documentation is
> https://www.wikidata.org/wiki/Help:Data_type#quantity but indeed there is
> no indication of the limit.
>
> From what I tested, apparently you can enter any number which is less than
> 127 characters long (https://www.wikidata.org/wiki/Q4115189#P1104).
>
> Cheers,
> ~nicolas
>
> Le lun. 7 oct. 2019 à 08:58, John Erling Blad  a écrit :
>
>> Is there any documentation of the number format used by the quantity
>> type? Bumped into this and had to implement the BCmath extension to handle
>> the number. The reason why I did it (except it was fun) is to handle some
>> weird unit conversions. By inspection I found there were numbers at
>> Wikidata that clearly could not be implemented as doubles, and testing a
>> little I found that this had to be implemented as some kind of big numbers.
>> Lua does not have big numbers, and using the numbers from quantity as a
>> plain number type is a coming disaster.
>>
>> So, is there any documentation for the quantity format anywhere? I have
>> not found anything. I posted a task about it, and please add info there if
>> you know where some info can be found. I suspect the format just happen to
>> be the same as BC, and nobody really checked if the format was compatible,
>> or…?
>>
>> The BCmath extension can be found at
>> - https://www.mediawiki.org/wiki/Extension:BCmath
>> - https://github.com/jeblad/BCmath
>>
>> There is a Vagrant role if anyone likes to test it out.
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Re: [Wikidata] Big numbers

[Jeroen De Dauw]

Hey John,

I'm not aware of any documentation, though there probably is some
somewhere. What I can point you to is the code dealing with numbers:
https://github.com/wmde/Number

Cheers

--
Jeroen De Dauw | www.EntropyWins.wtf  |
www.Professional.Wiki 
Entrepreneur | Software Crafter | Speaker | Open Souce and Wikimedia
contributor
~=[,,_,,]:3
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Re: [Wikidata] Big numbers

[Nicolas VIGNERON]

Hi,

The offical documentation is
https://www.wikidata.org/wiki/Help:Data_type#quantity but indeed there is
no indication of the limit.

>From what I tested, apparently you can enter any number which is less than
127 characters long (https://www.wikidata.org/wiki/Q4115189#P1104).

Cheers,
~nicolas

Le lun. 7 oct. 2019 à 08:58, John Erling Blad  a écrit :

> Is there any documentation of the number format used by the quantity type?
> Bumped into this and had to implement the BCmath extension to handle the
> number. The reason why I did it (except it was fun) is to handle some weird
> unit conversions. By inspection I found there were numbers at Wikidata that
> clearly could not be implemented as doubles, and testing a little I found
> that this had to be implemented as some kind of big numbers. Lua does not
> have big numbers, and using the numbers from quantity as a plain number
> type is a coming disaster.
>
> So, is there any documentation for the quantity format anywhere? I have
> not found anything. I posted a task about it, and please add info there if
> you know where some info can be found. I suspect the format just happen to
> be the same as BC, and nobody really checked if the format was compatible,
> or…?
>
> The BCmath extension can be found at
> - https://www.mediawiki.org/wiki/Extension:BCmath
> - https://github.com/jeblad/BCmath
>
> There is a Vagrant role if anyone likes to test it out.
> ___
> Wikidata mailing list
> Wikidata@lists.wikimedia.org
> https://lists.wikimedia.org/mailman/listinfo/wikidata
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[Wikidata] Big numbers

[John Erling Blad]

Is there any documentation of the number format used by the quantity type?
Bumped into this and had to implement the BCmath extension to handle the
number. The reason why I did it (except it was fun) is to handle some weird
unit conversions. By inspection I found there were numbers at Wikidata that
clearly could not be implemented as doubles, and testing a little I found
that this had to be implemented as some kind of big numbers. Lua does not
have big numbers, and using the numbers from quantity as a plain number
type is a coming disaster.

So, is there any documentation for the quantity format anywhere? I have not
found anything. I posted a task about it, and please add info there if you
know where some info can be found. I suspect the format just happen to be
the same as BC, and nobody really checked if the format was compatible, or…?

The BCmath extension can be found at
- https://www.mediawiki.org/wiki/Extension:BCmath
- https://github.com/jeblad/BCmath

There is a Vagrant role if anyone likes to test it out.
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