#13014: lcm for SR rationals
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Reporter: dsm | Owner: AlexGhitza
Type: enhancement | Status: closed
Priority: minor | Milestone: sage-5.2
Component: symbolics | Resolution: fixed
Keywords: sd40.5 | Work issues:
Report Upstream: N/A | Reviewers: Dan Drake, William Stein
Authors: Douglas McNeil | Merged in: sage-5.2.beta0
Dependencies: | Stopgaps:
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Comment (by dsm):
I think it should probably come out entirely. What seems to be going on
is that gcd is getting called during evaluation on a lot of floats, e.g.
{{{
sage: f = lambda t: 1/(t+pi)
sage: f(1.5r)
GCDing 1 <type 'int'> 1 0 <type 'int'> 0
returning on ZZ 1
GCDing 1.5 <type 'float'> 1.5 1.0 <type 'float'> 1.0
returning on QQ 1/2
GCDing 3.0 <type 'float'> 3.0 2.0 <type 'float'> 2.0
returning on ZZ 1
}}}
Previously, only integers would be tried, and they would typically (though
not always!) fail. Floats, however, can be coerced to QQ.. and so they
are. Sage is implicitly relying on the fact that gcd will fail, and fail
quickly, for floats. I can recover the original runtimes by adding more
explicit typechecks but that isn't very robust.
Far and away the simplest thing is to revert it, more's the pity. On the
bright side I probably exercise this code more than anyone else and even I
don't use it very much.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13014#comment:23>
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