# [Maxima] Half-angle-simplification of trig functions

Stavros Macrakis macrakis at alum.mit.edu
Wed Jan 7 09:20:32 CST 2009

```If assumptions like a<%pi/2 etc. aren't working properly, then it sounds as
though halfangles expansions will always be messy and hard to work with.

I would recommend that we do *not* release the new halfangle code until the
assume problem is resolved.

-s

On Wed, Jan 7, 2009 at 9:09 AM, Stefano Ferri <ferriste at gmail.com> wrote:

> I hope you'll find soon where is the bug :-)... For me it would be quite
> important if assume worked fine, because I am writing a code in wich I
> need to know the sign of trigonometric functions, and as of now there is
> no way to do it with an assumptions over angles without explicitly
> declaring the sign of sin, cos, and the others functions. I use this
> workarond for now. Strange is also that there are analogous problems
> with %e...
> Stefano
>
> > Hello Stefano,
> >
> > Yes I think it is the same problem.
> >
> > If I use an intervall (0,2*%pi) the simplification of sin(x/2) works
> well. If I
> > use an intervall (0,%pi) the simplifcation of cos(x/2) works well. But
> now the
> > simplification of sin(x/2) fails. If I use an intervall (0,3.0) both
> > simplifications works well.
> >
> > I think this is a bug of assume with %pi as a value. I do not know the
> reason of
> > the bug. I will have a deeper look into the code to find it.
> >
> > Dieter Kaiser
> >
>
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