From: jzakiya <jzakiya@...>
Date: 2009-12-24T09:45:25+09:00
Subject: Re: Trig value errors

On Dec 23, 1:05 pm, pharrington <xenogene...@gmail.com> wrote:
> On Dec 23, 12:35 pm, jzakiya <jzak...@mail.com> wrote:
>
>
>
> > Dear Matz,
>
> > I use a Linux calculator named Qaculate.
> > I do not know the people who designed and
> > coded it, but it makes me happy. Why?
>
> > When I put in sin(180) it outputs '0'
> > not 1.22460635382238e-16, and when I change
> > to radians for angles and do sin(PI) it
> > also gives '0' and not 1.22460635382238e-16.
>
> > This makes me happy.
>
> > In fact, this little Linux calculator produces
> > all the correct (exact) answers for angles on
> > an axis for both cos and sin, whether you input
> > the angles in degrees or radians. Astonishing!!
>
> > I don't now anything about how the people who
> > designed and implemented Qalculate decided to
> > use whatever language they chose to write it in,
> > or what libraries they decided to use. I don't
> > know (or care) about any of those under-the-hood
> > things.
>
> > What I do KNOW is that the people who designed and
> > implemented this calculator CARED that it produced
> > the mathematically exact results for those angles.
>
> > This makes me happy.
>
> > I use another add-on calculator for Firefox, called,
> > tada! Calculator. Again, I don't know the people who
> > designed and/or coded it, and I don't know what
> > language or libraries they used to do it in either.
> > But when I use this little calculator in Firefox I do
> > know I get sin(PI) = 0, not 1.22460635382238e-16.
>
> > So, for this calculator too, somebody(s) CARED enough
> > to make sure the answers came out correctly (exact)
> > for angles on an axis too. So when I use this calculator,
>
> > This makes me happy.
>
> > I think Ruby is a Great language, and a fun language.
> > And I agree with your philosophy that languages that
> > people use should serve them, not the other way around.
>
> > So I humbly tell you I am Surprised that Ruby produces
> > the math errors I've illustrated in this thread, and
>
> > This makes me unhappy.
>
> > So I am asking you to see that these errors be fixed.
>
> > If Qaculator and Calculator can produce the correct
> > results, then so can Ruby. All that is necessary is that
> > you CARE enough that it does it.
>
> > It would make me very happy if I could share my code, and
> > not have to include patches and redefinitions in it just
> > to assure other people get the same (exact) results I do.
>
> > I agree with your Principle of Least Surprises (POLS).
>
> > The language should work to please the user.
> > The language should be intuitive to the user.
> > The language should not cause unnecessary surprises.
>
> > So please, fix these errors.
>
> > This will make me happy.
>
> > Thanks
>
> Also, as an example:
>
> static VALUE
> math_cos(VALUE obj, VALUE x)
> {
>     Need_Float(x);
>     return DBL2NUM(cos(RFLOAT_VALUE(x)));
>
> }
>
> If you have a beef with anyone, its with the implementers of the C
> standard library, but...

Try this (with correct syntax if wrong).
Do similar for sin.

static VALUE
math_cos(VALUE obj, VALUE x)
{
    Need_Float(x);
    cos_value = DBL2NUM(cos(RFLOAT_VALUE(x)));
    if (abs(cos_value) < 1e-10) cos_value  0.0;
    return cos_value;
}