Function_cot.__evalf_() missing some cases

[burcin]

From this sage-support thread:

sage: u = cot(pi*x)
sage: u.is_zero()  
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<snip>
/home/burcin/sage/sage-5.11.beta3/local/lib/python2.7/site-packages/sage/functions/trig.pyc in _evalf_(self, x, parent)
    377         if parent is float:
    378             return 1/math.tan(x)
--> 379         return x.cot()
    380 
    381     def _derivative_(self, x, diff_param=None):
<snip>
AttributeError: 'sage.rings.complex_interval.ComplexIntervalFieldElement' object has no attribute 'cot'

There are many objects which end up as x in Function_cot._evalf_() that do not support .cot().

We should check if the other functions in sage/functions/trig.py handle more input types properly.

CC: @eviatarbach

Component: symbolics

Reviewer: Jeroen Demeyer

Issue created by migration from https://trac.sagemath.org/ticket/15179

[jdemeyer]

comment:4

worksforme:

sage: sage: u = cot(pi*x)
sage: sage: u.is_zero()  
False

[jdemeyer]

Reviewer: Jeroen Demeyer