[Python-ideas] Fwd: Trigonometry in degrees

[Nathaniel Smith]

On Tue, Jun 12, 2018, 00:03 Stephan Houben <stephanh42 at gmail.com> wrote:

> Hi all,
>
> I wrote a possible implementation of sindg:
>
> https://gist.github.com/stephanh42/336d54a53b31104b97e46156c7deacdd
>
> This code first reduces the angle to the [0,90] interval.
> After doing so, it can be observed that the simple implementation
>   math.sin(math.radians(angle))
> produces exact results for 0 and 90, and a result already rounded to
> nearest for
> 60.
>

You observed this on your system, but math.sin uses the platform libm,
which might do different things on other people's systems.


> For 30 and 45, this simple implementation is one ulp too low.
> So I special-case those to return the correct/correctly-rounded value
> instead.
> Note that this does not affect monotonicity around those values.
>

Again, monotonicity is preserved on your system, but it might not be on
others. It's not clear that this matters, but then it's not clear that any
of this matters...

-n
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