[sympy] add subfactorial function (#1692)
Christopher Smith
Why doesn't this get loaded into the sympy namespace along with all the other factorial frunctions? I don't understand how the __init__ file is working in this module.
You can merge this Pull Request by running:
git pull https://github.com/smichr/sympy subfact
Or view, comment on, or merge it at:
https://github.com/sympy/sympy/pull/1692
Commit Summary
- add subfactorial function
File Changes
- M sympy/functions/combinatorial/factorials.py (62)
- M sympy/functions/combinatorial/tests/test_comb_factorials.py (10)
- M sympy/utilities/iterables.py (4)
Patch Links
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Aaron Meurer
In sympy/functions/combinatorial/factorials.py:
> @@ -161,6 +163,64 @@ class MultiFactorial(CombinatorialFunction): > pass > > > +class subfactorial(CombinatorialFunction): > + """The subfactorial counts the derangements of n items and is > + defined for non-negative integers as:: > + > + , > + | 1 for n = 0 > + !n = | 0 for n = 1
This should be a { or < (and by the way, pprint(Piecewise, use_unicode=False) looks worse than this).
Aaron Meurer
You need to add it to sympy/functions/__init__.py. I also don't understand the purpose of the sympy/functions/combinatorial/__init__.py function.
Aaron Meurer
Add the standard links to Wikipedia and/or MathWorld (or any other good reference that you know of). The Wikipedia article seems to be pretty good.
Aaron Meurer
In sympy/functions/combinatorial/factorials.py:
> + @classmethod
> + def eval(cls, arg):
> + try:
> + arg = as_int(arg)
> + if arg < 0:
> + raise ValueError
> + return C.Integer(cls._eval(arg))
> + except ValueError:
> + if sympify(arg).is_Number:
> + raise ValueError("argument must be a nonnegative integer")
> +
> + def _sympystr(self, p):
> + if self.args[0].is_Atom:
> + return "!%s" % p.doprint(self.args[0])
> + else:
> + return "!(%s)" % p.doprint(self.args[0])
This needs other printers too, but I wonder if you can somehow just set the function name to ! somewhere, and have all printers automatically work.
Aaron Meurer
In sympy/functions/combinatorial/factorials.py:
> + @classmethod
> + def eval(cls, arg):
> + try:
> + arg = as_int(arg)
> + if arg < 0:
> + raise ValueError
> + return C.Integer(cls._eval(arg))
> + except ValueError:
> + if sympify(arg).is_Number:
> + raise ValueError("argument must be a nonnegative integer")
> +
> + def _sympystr(self, p):
> + if self.args[0].is_Atom:
> + return "!%s" % p.doprint(self.args[0])
> + else:
> + return "!(%s)" % p.doprint(self.args[0])
Except it doesn't use parentheses for atom arguments. So you still have to special case it. So please add the other printers. You need pretty print (ascii and unicode, should be the same) and LaTeX (and any others that might be useful).
Aaron Meurer
SymPy Bot Summary: 
Failed after merging smichr/subfact (afec347) into master (14452a4).
@smichr: Please fix the test failures.
Python 2.5.0-final-0: fail
Python 2.6.6-final-0: fail
Python 2.7.2-final-0: fail
Python 2.6.8-final-0: fail
Python 2.7.3-final-0: fail
PyPy 2.0.0-beta-1; 2.7.3-final-42: fail
Python 3.2.2-final-0: fail
Python 3.3.0-final-0: fail
Python 3.2.3-final-0: fail
Python 3.3.0-final-0: fail
Python 3.3.0-final-0: fail
**Sphinx 1.1.3:** pass
Aaron Meurer
SymPy Bot Summary: Failed after merging smichr/subfact (797dd34) into master (501534b).
@smichr: Please fix the test failures.
Python 2.5.0-final-0: fail
Python 2.6.6-final-0: fail
Python 2.7.2-final-0: fail
Python 2.6.8-final-0: fail
Python 2.7.3-final-0: fail
PyPy 2.0.0-beta-1; 2.7.3-final-42: fail
Python 3.2.2-final-0: fail
Python 3.3.0-final-0: fail
Python 3.2.3-final-0: fail
Python 3.3.0-final-0: fail
Python 3.3.0-final-0: fail
**Sphinx 1.1.3:** pass
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Christopher Smith
@asmeurer , printers and reference has been added.
Aaron Meurer
In sympy/functions/combinatorial/factorials.py:
> class factorial2(CombinatorialFunction):
> """The double factorial n!!, not to be confused with (n!)!
>
> The double factorial is defined for integers >= -1 as::
>
> - ,
> - | n*(n - 2)*(n - 4)* ... * 1 for n odd
> - n!! = -| n*(n - 2)*(n - 4)* ... * 2 for n even
> - | 1 for n = 0, -1
> - '
> + { n*(n - 2)*(n - 4)* ... * 1 for n odd
> + n!! = { n*(n - 2)*(n - 4)* ... * 2 for n even
That's not quite what I meant. I was thinking more
,
|
{
|
'
Really, though, none of them look very good. But we really should figure out what looks the best, and change the Piecewise ASCII pretty printer to use it.
Christopher Smith
I modified the docstring representation of the piecewise definition.
Julien Rioux
SymPy Bot Summary: Passed after merging smichr/subfact (dda5947) into master (d503614).
PyPy 2.0.0-beta-1; 2.7.3-final-42: pass
Python 2.7.2-final-0: pass
Python 3.2.1-final-0: pass
Sphinx 1.1.3: pass
Docs build command: make clean && make html-errors && make latex && cd _build/latex && xelatex sympy-*.tex
Aaron Meurer
This looks fine.
Christopher Smith
Thanks for looking this over. It's in.
Christopher Smith
Merged #1692.