```Issue #4897 has been updated by Simon Baird.

> At the developers' meeting this week, mrkn suggested `TWO_PI` instead.

I don't think TWO_PI would be very useful since it misses the main point of tau, which is that tau is the correct circle constant, (and pi is a 2000 year old blunder)[1]. If you consider this diagram [2] with TWO_PI in place of tau, then it loses its meaning.

Defining HALF_TAU could be useful though. ;)

[1] Of course not everyone agrees on this, but http://tauday.com/tau-manifesto is quite convincing IMO

[2] http://tauday.com/assets/figures/tau-angles.png

----------------------------------------
Feature #4897: Define Math::TAU and BigMath.TAU. The "true" circle constant, Tau=2*Pi. See http://tauday.com/
https://bugs.ruby-lang.org/issues/4897#change-60890

* Author: Simon Baird
* Status: Assigned
* Priority: Normal
* Assignee: Yukihiro Matsumoto
----------------------------------------
Firstly please read the Tau Manifesto at http://tauday.com/ . It's quite long but essential to understanding why this is a good idea.

Here is a patch on trunk that implements this:
http://simonbaird.blogspot.com/2011/06/tau-in-ruby.html

Allow me to anticipate and respond in advance to some common objections:

1. It's easy to define it yourself so why put this in core.
Possibly correct, but I think this is the right thing to do. Tau is important. And it's a pretty small patch.

2. If this constant goes in then pretty soon someone will want every other math constant and there are hundreds of them. (Slippery slope argument).
The circle constant is one of the two most important numbers is mathematics. It's not just another math constant. We already define Pi.

---Files--------------------------------
tau.patch (1.2 KB)
tau.patch (1.2 KB)

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