sympy/sympy — pull request #2988 by zanzibar7 (2014-03-02 19:11:37+00:00)
Title: Improve constant simplification for dsolve

- Fixes constant-collision errors in dsolve for good
- revise tests for ode, cse, pde, and constantsimp
- Constant numbering starts with C1, unless specified otherwise
- Specific checks for common subexpression and linear simplifications
- lie_group method errors appear because of x = Symbol('x',real=True)
We work around with x = Symbol('x'), which raises no errors.
- Extends cse (common subexpression elimination) to Piecewise,
and does not rewrite Order terms
- Poorly defined behavior of collect is causing problems internally
which extra code is added to handle.
- Stop classifying some nonlinear ODEs as linear.