Dear Nicolas,
If you do
sage: a = sin((a+b)/c)
sage: a.trig_expand??
you will see the source code, which simply uses one of Maxima's
expansion routines, whose behavior should be documented on the Maxima
Sourceforge site. My suspicion is that Maxima declines to expand this
because c might be zero, though there could be another reason. We
have several Maxima experts who also read this list and might have
more detailed information, but this would be the first place I would
start. One idea might be to apply another simplification/expansion to
whatever you feed into your trig functions, before you expand the
rest.
Good luck, and please follow up with more details, or specific
proposals for how we can improve our documentation to help make it
clearer how this works. Thank you!
- kcrisman
On Feb 2, 9:06 am, Nicolas <nicolas.fresseng...@gmail.com> wrote:
> Here is some to-my-opinion strange behaviour of trig_expand :
>
> #Declare real variables
> var('a b c')
> assume([a,'real'],[b,'real'],[c,'real'])
> assumptions()
> ---> [a is real, b is real, c is real]
>
> #Case 1
> sin(a+b).trig_expand()
> ---> sin(a)*cos(b) + sin(b)*cos(a)
>
> #Case 2
> sin((a+b)/2).trig_expand()
> ---> sin(1/2*a)*cos(1/2*b) + sin(1/2*b)*cos(1/2*a)
>
> #Case 3
> sin((a+b)/c).trig_expand()
> ---> sin((a + b)/c)
>
> #Case 4
> sin((a/c+b/c)).trig_expand()
>
> ________
> In case 3, the expansion is not done. I wonder if it would be possible
> to do it. Obviously, if the sine argument was rational expanded before
> trig expansion, it would work but none seem to work on the whole
> expression.
>
> Any idea ?
>
> PS: I am actually using this in an expression where doing this
> expansion would simplify a lot and I would have expected simplify_full
> to see it... which it does not, I suspect because of this.
> ---> sin(a/c)*cos(b/c) + sin(b/c)*cos(a/c)
--
To post to this group, send email to sage-support@googlegroups.com
To unsubscribe from this group, send email to
sage-support+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sage-support
URL: http://www.sagemath.org
