On Sunday, January 8, 2017 at 11:40:13 AM UTC+1, vdelecroix wrote: > > 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.
Please add your ideas to https://trac.sagemath.org/ticket/22155 > Would it be easy to make is_real works on builtin functions? > Yes, in C++ the code here is called with any function: https://github.com/pynac/pynac/blob/master/ginac/function.cpp#L1581 In Python, no. You would have to construct a second expression where any function of your choice is replaced with a e.g. constant that has the property you determined yourself on that function, and call is_real on that second expression. > 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 > Calling imag can be costly and I want to avoid that with all the is_ functions. -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
