From: Masahiro Tanaka <masa@...>
Date: 2000-09-22T03:29:55+09:00
Subject: [ruby-talk:5051] Re: Proposal: Add constants to Math

Hi,

> Since we now have Float#nan? and Float#infinite? I think the following
> constants should be added to Math (or Float?) for completeness:
> 
> NEGINF = Math.log(-1) # Or better way of generating NEGINF...
> INF = -NEGINF
> NAN = INF / INF

I can see discussion on Float::NaN and INFINITY in old mailing
list log ([ruby-dev:4760], etc.).  The problem is it may depend
on machine.  I do not know current status.


> A cautionary tale for users of dynamical languages such as Ruby:
> 
> I had the constant definitions above in a unit test file but the test
> cases kept failing no matter what I did. The problem was that I included
> the NArray extension which in turn included Complex which redefined
> Math.log so that it returned the correct complex number instead of
> -Infinity above. Makes you think before changing the behavior of methods
> in the standard distr... (and yes, I now know complex aliases Math.log to
> Math.log!)

I do not know how you use the NArray extension, but 
to avoid other readers confuse, I note:

* NArray function module is NMath, not Math.
* NMath.log(-1) returns -Infinity.

% irb -r narray
irb(main):001:0> NMath.log(-1)
-Infinity
irb(main):002:0> NMath.log(-1.0+0.im)
Complex(0.0, 3.141592654)

Masa Tanaka