error in limit involving exp, sinh and an assumption (maybe related to caching)

[Rüdiger Braun]

Hi all!

The following code

(compana16) braun:~/git/compana16$ ipython
Python 3.5.2 |Continuum Analytics, Inc.| (default, Jul  2 2016, 17:49:02)
Type "copyright", "credits" or "license" for more information.

IPython 5.1.0 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.

In [1]: import sympy

In [2]: sympy.__version__
Out[2]: '1.0'

In [3]: x = sympy.Symbol('x')

In [4]: a = sympy.Symbol('a', positive=True)

In [5]: f = sympy.exp(x*(-a-1)) * sympy.sinh(x)

In [6]: f.limit(x, sympy.oo)
Out[6]: oo

produces false output.  Correct is 0
I think it is somehow related to caching.  If caching is turned off, then the product in [5] cannot even be constructed.

(compana16) braun:~/git/compana16$ export SYMPY_USE_CACHE='no'
(compana16) braun:~/git/compana16$ ipython
Python 3.5.2 |Continuum Analytics, Inc.| (default, Jul  2 2016, 17:49:02)
Type "copyright", "credits" or "license" for more information.

IPython 5.1.0 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.

In [1]: import sympy

In [2]: sympy.__version__
Out[2]: '1.0'

In [3]: x = sympy.Symbol('x')

In [4]: a = sympy.Symbol('a', positive=True)

In [5]: f = sympy.exp(x*(-a-1))

In [6]: g = sympy.sinh(x)

In [7]: h = f*g
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
/home/braun/miniconda3/envs/compana16/lib/python3.5/site-packages/sympy/core/assumptions.py in getit(self)
    240         try:
--> 241             return self._assumptions[fact]
    242         except KeyError:

KeyError: 'zero'

During handling of the above exception, another exception occurred:

KeyError                                  Traceback (most recent call last)
/home/braun/miniconda3/envs/compana16/lib/python3.5/site-packages/sympy/core/assumptions.py in getit(self)
    240         try:
--> 241             return self._assumptions[fact]
    242         except KeyError:

KeyError: 'zero'

This goes on until a RecursionError kicks in.

Best regards

Rüdiger Braun

[Aaron Meurer]

Can you open an issue in the issue tracker for this?

Aaron Meurer

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[Francesco Bonazzi]

I think we should merge Kirpichev's fork into SymPy. He has fixed lots of issues with limits.

[Rüdiger Braun]

I opened a ticket under number

#11833

[Rüdiger Braun]

The problem is not present in Kirpichev's fork (diofant).