AssertionError plotting real part of complex function with float coefficients

[paulmasson]

Attempting this plot produces the error:

sage: plot(real(sqrt(x - 1.*I)), (x,0,1))
...
/Users/Masson/Downloads/GitHub/sage/src/sage/symbolic/pynac.pyx in sage.symbolic.pynac.py_atan2 (/Users/Masson/Downloads/GitHub/sage/src/build/cythonized/sage/symbolic/pynac.cpp:18694)()
   1740     from sage.symbolic.constants import pi
   1741     parent = parent_c(x)
-> 1742     assert parent is parent_c(y)
   1743     if parent is ZZ:
   1744         parent = RR

AssertionError: 

Reported in this ask question.

Component: symbolics

Author: Ralf Stephan, Paul Masson

Branch/Commit: 8c1e1eb

Reviewer: Paul Masson, Ralf Stephan

Issue created by migration from https://trac.sagemath.org/ticket/21428

[rwst]

Branch: u/rws/assertionerror_plotting_real_part_of_complex_function_with_float_coefficients

[rwst]

Commit: 13e72f3

[rwst]

New commits:

13e72f3

21428: be permissive in py_atan2

[rwst]

Author: Ralf Stephan

[paulmasson]

comment:3

Solves the plot problem, but needs doctests for arguments with different parents to illustrate the change.

Also, there are uncommitted changes for Pynac 0.6.9.1 that get included when this branch is checked out. They belong on another branch and ticket.

[paulmasson]

Reviewer: Paul Masson

[paulmasson]

comment:4

This simple change is likely to have future repercussions. Wouldn't it make more sense to determine both parents and use whichever is more general?

[rwst]

Changed branch from u/rws/assertionerror_plotting_real_part_of_complex_function_with_float_coefficients to none