Le 08/01/2017 à 09:42, Ralf Stephan a écrit :
On Sunday, January 8, 2017 at 9:14:15 AM UTC+1, Emmanuel Charpentier wrote:
Le dimanche 8 janvier 2017 08:48:33 UTC+1, Ralf Stephan a écrit :
You mean doing floating point computations to determine if an
expression is real?
Aaarghh..
That was tongue in cheek, sorry. Actually the cos case can be implemented
easily,
similarly to what we have done with
sage: log(pi/7).is_real()
True
Let's just ask, which functions result in any irreal with real argument,
not many I guess.
Making is_real works on the image of most functions would be good. It
would in particular let Sage recognize that cos(pi/7) is a real number.
Would it be easy to make is_real works on builtin functions?
However, an expression such as exp(I*pi/7) + exp(-I*pi/7) would still be
considered as not being real. Even if
sage: (exp(I*pi/7) + exp(-I*pi/7)).imag()
0
Please, put me in cc if you open related tickets.
Vincent
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