This mail is not directly related to removing the old assumptions, but
rather to the next steps after that.
One issue that comes up every now and then seems to be that we dislike,
in general, automatic simplification (and automatic evaluation).
Autosimplification uses the old assumptions system. For example.
In [1]: x = Symbol('x', positive=True)
In [2]: abs(x)
Out[2]: x
refine is the "new approach", using new assumptions:
In [3]: abs(y)
Out[3]: │y│
In [4]: refine(abs(y), Q.positive(y))
Out[4]: y
There is also the unify/ module, which I know nothing about.
Once the old assumptions system has been replaced by the new one, the
following question comes up naturally: in what form do we re-use the
(still existent) autosimplification code?
For example, we could implement a function which does "refinement using
autosimplification":
def autorefine(expr, facts):
with assuming(facts):
re-build the expr tree
return the new version
This seems like a good idea mid-term, but now we have refinement code
scattered through all the classes, and some refinement code separate.
This seems suboptimal. What should the long-term strategy be?
It seems to me that, eventually, the separate refine code should be so
easy to write that all of the autosimplification can be transcribed with
reasonable effort. Once we are there, we can remove the
autosimplification code, and make autosimplification optional (i.e. we
can implement some mechanism to optionally automatically refine newly
created objects). Most sympy modules will likely break with
autorefinement disabled, but one has to make a start somewhere. In
particular, now all the modules can transition at their own pace, and
some might decide never to do it.
Does this seem like a reasonable description of the consensus on
autosimplification?
Thanks,
Tom
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