#5152: order of abelian group element is a rational number, but should be an
integer
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Reporter: was | Owner: somebody
Type: defect | Status: new
Priority: minor | Milestone: sage-3.3
Component: basic arithmetic | Keywords:
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The line commented with "error here???" below is frightening:
{{{
File: /sage/groups/abelian_gps/abelian_group_element.py
Source Code (starting at line 268):
def order(self):
"""
Returns the (finite) order of this element or Infinity if this
element
does not have finite order.
EXAMPLES:
sage: F = AbelianGroup(3,[7,8,9]); F
Multiplicative Abelian Group isomorphic to C7 x C8 x C9
sage: F.gens()[2].order()
9
sage: a,b,c = F.gens()
sage: (b*c).order()
72
"""
M = self.parent()
if self == M(1):
return Integer(1)
invs = M.invariants()
if self in M.gens():
o = invs[list(M.gens()).index(self)]
if o == 0:
return infinity
return o
L = list(self.list())
N = LCM([invs[i]/GCD(invs[i],L[i]) for i in range(len(invs)) if
L[i]!=0]) ####### error here????
if N == 0:
return infinity
else:
return N
}}}
But what bugs me about it is:
{{{
sage: G = AbelianGroup(3,[7,8,9])
sage: type((G.0 * G.1).order())
<type 'sage.rings.rational.Rational'>
}}}
a simple coercion to Integer at the end of the function would fix this, or
using // instead of /. And add a doctest that has a type check so this
doesn't get re-introduced.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5152>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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