Re: Incorrect values of sin and cos

From: anshu khare (anshukhare1998_at_[hidden])
Date: 2020-01-17 01:52:02

On running cos(3*pi/2) , cos(5*pi/2) , cos(7*pi/2) , cos(9*pi/2)  all give
the same answer, which is less than epsilon except cos(7*pi/2) which gives
a highly negative value.

On Fri, 17 Jan, 2020, 5:41 AM Damian Vicino via Boost, <
boost_at_[hidden]> wrote:

> That's because pi is not pi but an approximation of it. When you multiply
> you amplify the error.
>
> On Thu, Jan 16, 2020, 18:48 anshu khare via Boost <boost_at_[hidden]>
> wrote:
>
> > Cos(pi/2) gives an exact zero.
> > Cos(3*pi/2) gives a value less than €.
> > But cos(7*pi/2) gives a large negative value which is not less than €.
> >
> > Anshu
> >
> > On Thu, 16 Jan, 2020, 11:29 PM John Maddock via Boost, <
> > boost_at_[hidden]> wrote:
> >
> > >
> > > On 16/01/2020 15:08, anshu khare via Boost wrote:
> > > > cos(3*pi(cpp_bin_float_50>()/2)) does not give correct value.
> > >
> > > What do you call "correct"?  If you're expecting an exact 0 result,
> then
> > > you're going to be disappointed - likewise with double which also does
> > > not yield an exact 0 in your test case (at least on msvc).
> > >
> > > John.
> > >
> > > > Only cos(pi(cpp_bin_float_50>()/2)) gives correct value.
> > > > All odd multiples of cos(pi/2) do not give correct value.
> > > >
> > > > The issue with sin() as well.
> > > >
> > > > Anshu
> > > >
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