This is my proposed patch
diff --git a/sympy/vector/coordsysrect.py b/sympy/vector/coordsysrect.py
index e5125d7..bfb00f9 100644
--- a/sympy/vector/coordsysrect.py
+++ b/sympy/vector/coordsysrect.py
@@ -438,6 +438,7 @@ def orient_new(self, name, orienters, location=None,
final_matrix = orienters.rotation_matrix(self)
else:
final_matrix = orienters.rotation_matrix()
+ final_matrix = trigsimp(final_matrix)
else:
final_matrix = Matrix(eye(3))
for orienter in orienters:
If there are no objections, I am going to apply this at
https://github.com/sympy/sympy/pull/10084, because it fixes the bug in
question.
Aaron Meurer
On Tue, Nov 10, 2015 at 3:46 PM, Aaron Meurer <[email protected]> wrote:
> Thanks for the fix Sachin.
>
> Now I'm hitting a new error. scalar_map calls trigsimp
> (https://github.com/sympy/sympy/blob/4bf728685a82c990d48624b482907d3cfa2d1fc2/sympy/vector/coordsysrect.py#L329),
> which causes some tests to fail because the matrix changes form (it
> starts with sin(q)*sqrt(3) - cos(q) and ends up with -2*cos(q +
> pi/3)). The problem is that the expressions otherwise look the same.
> It's just the CoordinateSystems buried in the BaseScalar objects that
> have different matrices.
>
> You can reproduce the issue by running
>
> ./bin/test sympy/vector/tests/test_coordsysrect.py
>
> in my python35 branch (https://github.com/sympy/sympy/pull/10084).
>
> I don't know what the correct fix here. I'm guessing trigsimp should
> have been called when the original C was created (in orient_new_axis),
> but I'm unsure.
>
> Aaron Meurer
>
> On Tue, Nov 10, 2015 at 6:25 AM, Sachin Joglekar
> <[email protected]> wrote:
>> An attempt to fix the issues here: https://github.com/sympy/sympy/pull/10130
>> . Also added tests to ensure that we test this part of compatibility with
>> the core, in any further work done to sympy.vector.
>>
>> On Tue, Nov 10, 2015 at 1:51 PM, Francesco Bonazzi <[email protected]>
>> wrote:
>>>
>>>
>>>
>>> On Tuesday, 10 November 2015 00:04:39 UTC+1, Aaron Meurer wrote:
>>>>
>>>> I'm trying to fix sympy.vector.Point so that it follows the args
>>>> invariant. Right now, there is a check that the parent_point must be a
>>>> Point instance, but it can also be None, in which case, it is set to a
>>>> Symbol. This causes a Point constructed in such way to not follow
>>>> expr.func(*expr.args) == expr.
>>>
>>>
>>> There are also some subclassing of Symbol and ignoring the parameter
>>> extensions:
>>>
>>> https://github.com/sympy/sympy/blob/01b4f8d97be55746ee2abe38163b533ca5318ba7/sympy/vector/scalar.py#L14
>>>
>>> index and system are defining parameters, they should be in the .args.
>>>
>>> Perhaps one should follow the example in sympy.diffgeom,
>>>
>>> https://github.com/sympy/sympy/blob/f3de4f3698c28355d6397e917b3d9d5bbf9c84c0/sympy/diffgeom/diffgeom.py#L467
>>>
>>> BaseScalarField in diffgeom is the analogous of BaseField in vector.
>>>
>>>>
>>>> Example:
>>>>
>>>> In [11]: from sympy.vector import *
>>>>
>>>> In [12]: C = CoordSysCartesian('C')
>>>>
>>>
>>> If I remember correctly, the letter 'C' (the name of the coordinate
>>> system) doesn't get registered in the args, that's another issue.
>>>
>>>>
>>>>
>>>> As a side note, the fact that this sort of thing exists in SymPy is
>>>> embarrassingly bad. We should fix test_args to test that objects are
>>>> recreatable from their arguments and put a moratorium on new objects
>>>> that don't follow that rule.
>>>>
>>>
>>> It's a bit complicated to explain to new users how to write class
>>> constructors.
>>>
>>> Mathematica has a pattern matching syntax that forces you to keep its
>>> equivalent of SymPy's args sorted in this particular way.
>>
>>
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