trigsimp does not simplify test case

[coxep]

(Edited to actually demonstrate the issue)

I am running SymPy 1.4 in Python 2.7. I have confirmed that this issue is also present in SymPy Live Shell.

I have a simple trigonometric expression that I am trying to simplify:

from sympy import sin, cos, symbols, trigsimp
x_0, y_0, theta_0 = symbols("x_0 y_0 theta_0")
trigsimp((x_0*cos(2*theta_0) + x_0 + y_0*sin(2*theta_0))/(2*cos(theta_0)))

Expected simplification:
x_0 * cos(theta_0) + y_0 * sin(theta_0)

Actual simplification (no change):
(x_0 * cos(2 * theta_0) + x_0 + y_0 * sin(2 * theta_0)) / (2 * cos(theta_0))

[ethankward]

I just tried this:

Python 2.7.12 (default, Oct  8 2019, 14:14:10) 
[GCC 5.4.0 20160609] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sympy
>>> sympy.__version__
'1.4'
>>> from sympy import *
>>> from sympy.abc import x, y, theta
>>> trigsimp((x * cos(2 * theta) + x + y * sin(2 * theta)) / (2 * cos(theta)))
x*cos(theta) + y*sin(theta)

Any other details?

[coxep]

Oops, looks like I left an important piece out.

This works great:

from sympy import sin, cos, symbols, trigsimp
x_0, y_0, theta_0 = symbols("x0 y0 theta0")
trigsimp((x_0*cos(2*theta_0) + x_0 + y_0*sin(2*theta_0))/(2*cos(theta_0)))

This does not:

from sympy import sin, cos, symbols, trigsimp
x_0, y_0, theta_0 = symbols("x_0 y_0 theta_0")
trigsimp((x_0*cos(2*theta_0) + x_0 + y_0*sin(2*theta_0))/(2*cos(theta_0)))

The issue seems to occur when using underscores in string variable names, at least in this instance.

No issue here, though:

from sympy import sin, cos, symbols, trigsimp
x_0, y_0, theta_0 = symbols("x_0 y_0 theta_0")
trigsimp(x_0 * cos(theta_0) **2 + x_0 * sin(theta_0) ** 2)