The last time I checked (last year) SymEngine doesn't support assumptions on Symbol objects.

Unfortunately we really need the Positive assumption, otherwise units like sqrt(g^2) won't simplify.

I'll check in with the SymEngine people next week at SciPy to see what progress has been made on that.

On Thu, Jul 6, 2017 at 3:21 PM, Matthew Turk <matthewturk@gmail.com> wrote:
Hi Nathan,

Have you tried out SymEngine with it?

On Thu, Jul 6, 2017 at 3:18 PM, Nathan Goldbaum <nathan12343@gmail.com> wrote:
> Hi all,
>
> I tested yt with the release candidate and didn't run into any issues. We're
> using very stable parts of the sympy API so I'm not expecting breakage. That
> said, if anyone notices issues related to this please let me know and I will
> fix ASAP.
>
> -Nathan
>
> ---------- Forwarded message ----------
> From: Aaron Meurer <asmeurer@gmail.com>
> Date: Thu, Jul 6, 2017 at 3:15 PM
> Subject: [sympy] SymPy 1.1 is released
> To: "sympy@googlegroups.com" <sympy@googlegroups.com>
>
>
> I'm happy to announce that SymPy 1.1 has been released. You can install it
> with
>
>     pip install -U sympy
>
> It also be available via conda soon.
>
> This is a major release of SymPy, with many major changes since the
> previous version, 1.0. The release notes are at
> https://github.com/sympy/sympy/wiki/Release-Notes-for-1.1 (note, at
> the time of this writing, these are still being updated).
>
> Please report any bugs you find in our issue tracker
> https://github.com/sympy/sympy/issues
>
> Some highlights (if I am missing anything major, please let me know
> and update the release notes page):
>
> - Many improvements to code generation, including addition of
> tensorflow (to lambdify), C++, llvm JIT, and Rust language support, as
> well as the beginning of AST classes.
>
> - Experimental support for SymEngine as a symbolic core in the
> sympy.physics.mechanics module (set the environment variable
> USE_SYMENGINE=1).
>
> - A reworking of the internals of the matrices module.
>
> - Several bug fixes for floating point numbers using higher than the
> default precision.
>
> In addition, several improvements from the 2016 Google Summer of Code
> projects, including:
>
> - A new holonomic submodule, for computing with holonomic functions
> (Shubham Tibra's GSoC project).
>
> - Improvements to the group theory module (Gaurav Dhingra's GSoC project).
>
> - Improvements to the solvers and solveset (Shekhar Prasad Rajak and
> Kshitij Saraogi's GSoC projects).
>
> - Implementation of Singularity Functions to solve Beam Bending
> problems (Sampad Kumar Saha's GSoC project).
>
> - Improvements to the mechanics module (James Brandon Milam's GSoC project).
>
> Thank you to everyone who contributed to this release. A full list of
> people who contributed is at
> https://github.com/sympy/sympy/wiki/Release-Notes-for-1.1#authors. A
> total of 184 people contributed to this release. Of these, 143 people
> contributed to SymPy for the first time for this release.
>
> Aaron Meurer
>
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