From: Benoit Daloze <eregontp@...>
Date: 2009-12-24T04:53:34+09:00
Subject: Re: Trig value errors

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If you want more precision, you could use BigDecimal (and BigMath).
Then you would get something like:

irb(main):025:0> p=2000; cos(PI(p)/2, p).to_s
=> "0.64773210554205705...E-2016"
irb(main):026:0> p=2000; sin(PI(p)/2, p).to_s
=> "0.99999999999999999999999999999999999999...E0"

Well, I think it's safe to round the 2016th decimal, isn't it ?
Also rounding a ton of 9.

So, rounding to the precision(2000), you get what you want.

irb(main):036:0> p=20; cos(PI(p)/2, p).round(p).to_f
=> 0.0
irb(main):037:0> p=20; sin(PI(p)/2, p).round(p).to_f
=> 1.0

And well, you really don't need 2000 of precision, 20 is far enough in this
case.


2009/12/23 Phrogz <phrogz@mac.com>

> On Dec 23, 12:11 am, jzakiya <jzak...@mail.com> wrote:
> > > On Dec 22, 10:07 pm, Phrogz <phr...@mac.com> wrote:
> > > > 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
>
> > This didn't nullify THE POINT I illustrated, which was
> > using an increasingly smaller angle approaching zero as
> > an argument, it eventually produced a value of '1' for
> > cos, but not '0' for the same sin angle, as it should.
>
> No, it didn't produce a value of 1. Look at the second part of my
> post, which you quoted, at the top of this message.
>
>

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