Define the TAU circle constant [Feature #4897] #644

simonbaird · 2014-06-28T08:33:41Z

Define TAU constant in math.c similar to PI.
Define TAU method in bigdecimal/math based on existing
PI method.

simonbaird · 2014-06-28T08:37:05Z

I tested like this:

oubliette:~/dev/ruby> [trunk_define_tau] /usr/local/bin/ruby -r bigdecimal/math -e 'puts Math::PI, BigMath.PI(20), Math::TAU, BigMath.TAU(20)'
3.141592653589793
0.3141592653589793238462643383279502884519859293521427E1
6.283185307179586
0.6283185307179586476925286766559005769039718587042854E1

simonbaird · 2014-06-28T08:38:41Z

Link to issue tracker:
https://bugs.ruby-lang.org/issues/4897

simonbaird · 2014-06-28T08:40:17Z

ext/bigdecimal/lib/bigdecimal/math.rb

@@ -180,7 +181,7 @@ def atan(x, prec)
  #   #=> "0.3141592653589793238462643388813853786957412E1"
  #
  def PI(prec)
-    raise ArgumentError, "Zero or negative argument for PI" if prec <= 0
+    raise ArgumentError, "Zero or negative precision for PI" if prec <= 0


Let me know if you don't like this. I'm happy to leave it as 'argument' if that is preferred. My thoughts are that precision is a better word and it is consistent with the message in the E method below.

* ext/bigdecimal/lib/bigdecimal/math.rb (BigMath#PI): change error message about zero or negative precision for clarity and consistency with other methods. [GH-644] git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46600 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

simonbaird · 2014-06-28T11:42:37Z

Rebased on top of 38f0133 "bigdecimal/math.rb: error message in BigMath#PI"

thoran · 2014-07-06T08:15:06Z

Simon, I think you've erred in putting PI first. Shouldn't TAU be first? Or perhaps they should be in alphabetical order: E, PI, TAU? Thanks for this patch and raising my awareness of Tau. I'm a Tau convert now too...

simonbaird · 2014-07-19T03:50:25Z

@thoran (Not sure if you're totally serious, but) I don't think changing the order is necessary or sensible. Glad to hear Tau has another convert.. :)

* ext/bigdecimal/lib/bigdecimal/math.rb (BigMath#PI): change error message about zero or negative precision for clarity and consistency with other methods. [rubyGH-644] git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46600 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

* math.c: Define TAU constant in similar to PI constant. * ext/bigdecimal/lib/bigdecimal/math.rb: Define TAU method in bigdecimal/math based on existing PI method.

mrkn · 2015-07-09T13:45:07Z

@simonbaird Please tell me how popular is tau in the community of mathematicians and physicians. I don't have any idea of it. I want to know how many research papers or textbooks using this new constant definition have been published as of today.

simonbaird · 2015-07-10T05:37:16Z

@mrkn Take a look here. It shows a year by year list of Tau related highlights including some books and publications that use it.

simonbaird · 2015-07-10T05:39:09Z

Google calculator has Tau: https://www.google.com/search?q=tau+%2B+0

gogotanaka · 2015-07-10T06:53:03Z

@simonbaird Hi! Thank you for working on it. While leaving a decision to @mrkn san, let me say something here.

Tau makes more sense than pi to me and is important constant as you show. I personally love this number.
But I really doubt whether it worth having tau as constant in Ruby. There are a lot of other math constants which are also important. And E and PI are top two of special one, very special. While Nobody complain about having E and PI as constant, discussing about how important other constants(Tau) is and worth it are kind of difficult.

simonbaird · 2015-07-13T00:00:03Z

The two most important constants in mathematics are e and "the circle constant". And, (according to the Tau supporters, myself included), the circle constant is Tau. So that's why I don't think the "slippery slope" argument, i.e. "if we add Tau then people will want to add many other constants" is valid.

Nevertheless, I understand the decision about whether to merge this is not a clear one. Here's some of my thoughts why it could be merged:

It won't hurt anyone
It can help further the acceptance and adoption of Tau (which I believe is a good thing for the world)

How about asking "why not" instead of "why"?

mrkn · 2015-07-20T23:01:33Z

@simonbaird I decided to reject this proposal. The reasons is:

It looks to me that tau as the circle constant isn't popular enough to be introduced in Ruby's core although it has good property.
So introducing tau is hurt the future Ruby now. Core constants cannot remove easily.
It's not Ruby's role to help further the acceptance and adoption of tau.
I found that Python and Julia rejected similar proposals. See https://bugs.python.org/issue12345 and WIP – tau: add MathConst{:τ} JuliaLang/julia#4864.

simonbaird · 2015-07-21T00:39:50Z

Okay, your reasoning is very sensible and well explained. Thanks very much for the consideration. Best wishes, Simon.

waldyrious · 2017-02-10T21:55:39Z

I found that Python and Julia rejected similar proposals. See https://bugs.python.org/issue12345 and JuliaLang/julia#4864.

Just FYI, Python actually ended up incorporating the proposal: issue 12345 is now marked as solved -- by Guido himself, no less :)

renewooller · 2025-01-05T03:35:37Z

Can we please reopen this issue? even iOS messenger and google calculator has TAU now... It makes a lot of maths easier and more intuitive because the definition for the circle constant is then based on radius rather than diameter, same as radians.

mrkn · 2025-01-05T04:16:04Z

even iOS messenger and google calculator has TAU now...

@renewooller I’m not sure how to use TAU in the iOS messenger, and I haven’t been able to confirm whether Google’s calculator supports TAU. As far as I can tell, both Google’s web calculator and Chrome’s built-in calculator only offer pi.

Could you please let me know how I can verify that TAU is available in these calculators?

By the way, the only criterion for deciding whether TAU can be included as a constant in the Math module is how frequently it appears in academic mathematics papers.

simonbaird reviewed Jun 28, 2014
View reviewed changes

sorah force-pushed the trunk branch from 5317131 to 307198a Compare November 26, 2014 12:13

Define the TAU circle constant [Feature ruby#4897]

2b8f97f

* math.c: Define TAU constant in similar to PI constant. * ext/bigdecimal/lib/bigdecimal/math.rb: Define TAU method in bigdecimal/math based on existing PI method.

simonbaird force-pushed the trunk_define_tau branch from 2661af9 to 2b8f97f Compare July 2, 2015 05:02

hsbt assigned mrkn Jul 9, 2015

mrkn closed this Jul 20, 2015

ericqweinstein mentioned this pull request Nov 17, 2017

Add Tau as a constant to math.c #1761

Closed

Define the TAU circle constant [Feature #4897] #644

Define the TAU circle constant [Feature #4897] #644

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simonbaird commented Jun 28, 2014

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