From: Phrogz <phrogz@...>
Date: 2009-12-23T14:10:28+09:00
Subject: Re: Trig value errors

On Dec 22, 7:08 pm, jzakiya <jzak...@mail.com> wrote:
> Hardware: 32-bit Intel P4 cpu
[snip]
> Ruby 1.9.1p243 output below
>
> 1)onedegree =2*PI/360 =>0.0241660973353061

Seriously? I don't believe it. Here's what I get:

irb(main):001:0> RUBY_VERSION
=> "1.9.1"
irb(main):002:0> include Math
=> Object
irb(main):003:0> onedegree = 2*PI/360
=> 0.0174532925199433

That's HUGELY different from the value you get. I am now suspicious of
the rest of your results.

> 6)cos onedegree/1e06  =>1.0

Sort of. Here's what I get:

irb(main):004:0> x = cos(onedegree/1e06)
=> 1.0
irb(main):005:0> x - 1.0
=> -1.11022302462516e-16
irb(main):006:0> puts "%.30f" % x
0.999999999999999888977697537484


> Examples 4)-9) show that at some point for cos a
> decision was made to fix (roundoff.truncation,?)
> cos(of a very smal number) = 1.0

False. What they show is that the string representation of floating
point values doesn't always show you the full picture.