As a test for the unit system module, I have written some codes using the
solve method, since Units (and other objects defined in the module) are
supposed to behave as normal sympy objects.
But when I call solve, it tries to create an intermediate Unit object where
one of the argument is Dummy, so it returns an error since this argument
should be a Unit or a Dimension object [2]. I tried to understand how solve
is working, but I don't get it. Here is the full traceback
File
"/mnt/data/Documents/Projets/Programmation/sympy/doc/src/modules/physics/unitsystems/examples.rst"
, line 76, in examples.rst
Failed example:
Tr = solve(T**2/venus_a**3 - 4*pi**2 / mks["G"] / solar_mass, T)[1]
Exception raised:
Traceback (most recent call last):
File "/usr/lib/python2.7/doctest.py", line 1289, in __run
compileflags, 1) in test.globs
File "<doctest examples.rst[25]>", line 1, in <module>
Tr = solve(T**2/venus_a**3 - 4*pi**2 / mks["G"] / solar_mass, T)[1]
File "sympy/solvers/solvers.py", line 893, in solve
f[i] = nsimplify(fi, rational=True)
File "sympy/simplify/simplify.py", line 3830, in nsimplify
return _real_to_rational(expr, tolerance)
File "sympy/simplify/simplify.py", line 3785, in _real_to_rational
return p.subs(reps, simultaneous=True)
File "sympy/core/basic.py", line 941, in subs
rv = rv._subs(old, d, **kwargs)
File "sympy/core/cache.py", line 93, in wrapper
r = func(*args, **kw_args)
File "sympy/core/basic.py", line 1063, in _subs
rv = fallback(self, old, new)
File "sympy/core/basic.py", line 1035, in fallback
arg = arg._subs(old, new, **hints)
File "sympy/core/cache.py", line 93, in wrapper
r = func(*args, **kw_args)
File "sympy/core/basic.py", line 1063, in _subs
rv = fallback(self, old, new)
File "sympy/core/basic.py", line 1035, in fallback
arg = arg._subs(old, new, **hints)
File "sympy/core/cache.py", line 93, in wrapper
r = func(*args, **kw_args)
File "sympy/core/basic.py", line 1063, in _subs
rv = fallback(self, old, new)
File "sympy/core/basic.py", line 1035, in fallback
arg = arg._subs(old, new, **hints)
File "sympy/core/cache.py", line 93, in wrapper
r = func(*args, **kw_args)
File "sympy/core/basic.py", line 1063, in _subs
rv = fallback(self, old, new)
File "sympy/core/basic.py", line 1040, in fallback
rv = self.func(*args)
File "sympy/physics/unitsystems/units.py", line 72, in __new__
"instance; found %s" % type(dim))
TypeError: 'dim' object should be Unit or Dimension instance; found <
class 'sympy.core.symbol.Dummy'>
When I wrote the test (commit 05ddf1aeac22eb1f01c9db1c7ab61d6ee8cc955b),
this was working since I just copied-pasted the results I was seeing on
IPython. One of the main thing which change since this moment is that Unit
inherits from Expr instead of AtomicExpr. I tried to go back to the
mentioned commit, but now I get a recursive call...
This is the only remaining bug in the proposed pull request [3]. You can
find the branch there [4].
Do you have some ideas? if not, maybe we should give up (temporarily) the
use of Units in equations, etc. (since we can still do it with abstract
symbol and then replace).
[1]
https://github.com/melsophos/sympy/blob/units/doc/src/modules/physics/unitsystems/examples.rst
[2]
https://github.com/melsophos/sympy/blob/units/sympy/physics/unitsystems/units.py
[3] https://github.com/sympy/sympy/pull/2628
[4] https://github.com/melsophos/sympy/tree/units
Best,
Harold
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