Christopher Smith

I am surprised that we have the `div` function in the namespace by default with little documentation and no warning in documentation about using it for multivariate expressions.

needs a test added for this issue

> not sure if there is any option from `Expr` to perform this sort of substitution. ```python >>> (x**3).extract_multiplicatively(x**2)*y x*y ``` If the extraction is not possible then an error...

> This isn't sufficient when there are additive terms and I don't need the factorization. It was just a suggestion of how you can test to see if `old` can...

Here is an example of a routine that would do what you are describing for integer powers: it tries partial integer extraction after the regular subs attempt: ```python def psubs(eq,...

This hasn't been active for a while, but have you looked at the Centripetal Catmull-Rom spline? Here it is applied separately to the x and y coordinate of points in...

``` sift comsumes and stores the entire iterable: m = defaultdict(list) for i in seq: m[keyfunc(i)].append(i) return m ``` Original comment: http://code.google.com/p/sympy/issues/detail?id=3898#c1 Original author: https://code.google.com/u/117933771799683895267/

The linked code is for binary sifting into predicate true and false and lazily consumes the iterable. It might be worth a separte function if sift results could be more...

``` With the FU routines of https://github.com/sympy/sympy/pull/1737 you can selectively rewrite something like 1/cos(x)**-2 >>> TR16(1/cos(x)**2) tan(x)**2 + 1 ``` Original comment: http://code.google.com/p/sympy/issues/detail?id=1201#c8 Original author: https://code.google.com/u/117933771799683895267/

failing: `File "/simplify/tests/test_hyperexpand.py", line 687, in test_prudnikov_misc: assert can_do([a], [a - S.Half, 2*a + 1])`