sympy/sympy — pull request #717 by smichr (2011-11-16 06:18:34+00:00)
Title: let nsimplify select tolerance and autodetect rational case

nsimplify is meant to convert numbers into alternate forms;
sometimes one just wants Rationals for Floats. The rational
flag can be used to do this, but if the expression contains
symbols (i.e., is not a number) then the rational flag is automatically
selected.

In addition, the tolerance is set to the highest tolerance of the
numbers appearing in the expression if none is given.

see issues:
http://code.google.com/p/sympy/issues/detail?id=1975
http://code.google.com/p/sympy/issues/detail?id=2100