From: Seebs <usenet-nospam@...>
Date: 2009-12-24T09:50:09+09:00
Subject: Re: Trig value errors

On 2009-12-24, jzakiya <jzakiya@mail.com> wrote:
> 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;
> }

That'd be exceptionally stupid.

Here's the problem:  There exists at least one value for which the correct
value of cos(x) is about 9e-11, which can be correctly represented (within
a much, much, smaller margin of error) in a floating point value, and which
you would then "fix" by changing it from not-zero to exactly-zero.

Which is to say, this would introduce a comparatively HUGE error, much larger
than the alleged error you're complaining about.

If you want approximate values, round them.

-s
-- 
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