[Python-ideas] Fwd: Trigonometry in degrees
Steven D'Aprano
steve at pearwood.info
Sat Jun 16 09:27:24 EDT 2018
On Thu, Jun 14, 2018 at 01:44:34PM -0500, Tim Peters wrote:
> I should note that numeric code "that works" is often much subtler than it
> appears at first glance. So, for educational purposes, I'll point out some
> of what _wasn't_ said about this crucial function:
[...]
Thanks Tim!
Reading your digressions on the minutia of floating point maths is
certainly an education. It makes algebra and real-valued mathematics
seem easy in comparison.
I still haven't got over Mark Dickinson's demonstration a few years
back that under Decimal floating point, but not binary, it is possible
for the ordinary arithmetic average (x+y)/2 to be outside of the
range [x, y]:
py> from decimal import getcontext, Decimal
py> getcontext().prec = 3
py> x = Decimal('0.516')
py> y = Decimal('0.518')
py> (x + y) / 2
Decimal('0.515')
--
Steve
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