# Confusing docs . . . how do I use gcd2?

**URL:** <https://www.ruby-forum.com/t/confusing-docs-how-do-i-use-gcd2/181335>\
**Category:** Ruby\
**Created:** [January 10, 2010, 2:35am UTC](https://www.ruby-forum.com/t/confusing-docs-how-do-i-use-gcd2/181335 "2010-01-10T02:35:47Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![javamllama](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ce7236/32.png) [@javamllama](https://www.ruby-forum.com/u/javamllama)\
**Post date:** [January 10, 2010, 2:35am UTC](https://www.ruby-forum.com/t/confusing-docs-how-do-i-use-gcd2/181335/1 "2010-01-10T02:35:47Z")

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The standard library docs don’t make sense to me a lot of the time.  
How do I use the gcd2 method in class Integer (or is it in file  
mathn.rb . . . no idea)?

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**Author:** ![javamllama](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ce7236/32.png) [@javamllama](https://www.ruby-forum.com/u/javamllama)\
**Post date:** [January 10, 2010, 2:36am UTC](https://www.ruby-forum.com/t/confusing-docs-how-do-i-use-gcd2/181335/2 "2010-01-10T02:36:22Z")

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On Jan 9, 8:32 pm, Matt [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> The standard library docs don’t make sense to me a lot of the time.  
> How do I use the gcd2 method in class Integer (or is it in file  
> mathn.rb . . . no idea)?

Here’s a link to what I’m looking at:  
[http://www.ruby-doc.org/stdlib/libdoc/mathn/rdoc/classes/Integer.html#M000926](http://www.ruby-doc.org/stdlib/libdoc/mathn/rdoc/classes/Integer.html#M000926)

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**Author:** ![javamllama](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ce7236/32.png) [@javamllama](https://www.ruby-forum.com/u/javamllama)\
**Post date:** [January 10, 2010, 3:55am UTC](https://www.ruby-forum.com/t/confusing-docs-how-do-i-use-gcd2/181335/3 "2010-01-10T03:55:21Z")

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Matt wrote:

> On Jan 9, 8:32 pm, Matt [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:
> 
> > The standard library docs don’t make sense to me a lot of the time.  
> > How do I use the gcd2 method in class Integer (or is it in file  
> > mathn.rb . . . no idea)?
> 
> Here’s a link to what I’m looking at:  
> [http://www.ruby-doc.org/stdlib/libdoc/mathn/rdoc/classes/Integer.html#M000926](http://www.ruby-doc.org/stdlib/libdoc/mathn/rdoc/classes/Integer.html#M000926)

Are you using 1.8.x or 1.9.x? The method is defined in mathn.rb for 1.8  
but not for 1.9.

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**Author:** ![javamllama](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ce7236/32.png) [@javamllama](https://www.ruby-forum.com/u/javamllama)\
**Post date:** [January 10, 2010, 4:02am UTC](https://www.ruby-forum.com/t/confusing-docs-how-do-i-use-gcd2/181335/4 "2010-01-10T04:02:58Z")

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Justin C. wrote:

> > 
> 
> =\> 4
> 
> -Justin

Sorry, that should be gcd2.

-Justin

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**Author:** ![javamllama](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ce7236/32.png) [@javamllama](https://www.ruby-forum.com/u/javamllama)\
**Post date:** [January 10, 2010, 4:20am UTC](https://www.ruby-forum.com/t/confusing-docs-how-do-i-use-gcd2/181335/5 "2010-01-10T04:20:31Z")

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Justin C. wrote:

> > > 
> > 
> > -Justin
> 
> Sorry, that should be gcd2.
> 
> -Justin

For your information gcd works with 1.9.1 but gcd2 does not. Not sure  
what the difference between gcd and gcd2 are and why gcd2 was dropped  
from mathn in 1.9.1.

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**Author:** ![javamllama](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ce7236/32.png) [@javamllama](https://www.ruby-forum.com/u/javamllama)\
**Post date:** [January 10, 2010, 4:02am UTC](https://www.ruby-forum.com/t/confusing-docs-how-do-i-use-gcd2/181335/6 "2010-01-10T04:02:23Z")

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Matt wrote:

> 

Both, sort of.

ruby 1.8.7 (2008-08-11 patchlevel 72) [i686-linux]

irb(main):001:0\> require ‘mathn’  
=\> true  
irb(main):002:0\> 12.gcd(4)  
=\> 4

-Justin

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**Author:** ![javamllama](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ce7236/32.png) [@javamllama](https://www.ruby-forum.com/u/javamllama)\
**Post date:** [January 10, 2010, 4:46am UTC](https://www.ruby-forum.com/t/confusing-docs-how-do-i-use-gcd2/181335/7 "2010-01-10T04:46:17Z")

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Michael W. Ryder wrote:

> > > > [http://www.ruby-doc.org/stdlib/libdoc/mathn/rdoc/classes/Integer.html#M000926](http://www.ruby-doc.org/stdlib/libdoc/mathn/rdoc/classes/Integer.html#M000926)  
> > > > =\> 4  
> > > > from mathn in 1.9.1.

I don’t know, exactly, either.  
Here is the thread referenced by the changelog:  
[http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-core/7931](http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-core/7931)

-Justin