#4850: bug in power_mod
------------------------------+---------------------------------------------
Reporter: was | Owner: somebody
Type: defect | Status: new
Priority: major | Milestone: sage-3.2.3
Component: basic arithmetic | Keywords:
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{{{
----------------------------------------------------------------------
| SAGE Version 3.1.4, Release Date: 2008-10-16 |
| Type notebook() for the GUI, and license() for information. |
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sage: power_mod(11,1,7)
11
sage: mod(11^1,7)
4
sage: # Hmmm...???
sage:
...al
}}}
Note above that power_mod(11,1,7) should return 4. The fix is to look at
the *pure python* code that defines power_mod in rings/arith.py and:
1. change it to use some much more intelligent compiled code, i.e.,
either the powermod or powermod_ui methods when the first input coerces to
ZZ, and
2. when a doesn't coerce to ZZ, just revert to the existing Python code,
but make sure to throw in an {{{%m}}} somewhere before returning the
answer.
3. Add a doctest like this that illustrates non-integer input for the
first argument to power_mod:
{{{
sage: power_mod(3*x, 10, 7)
4*x^10
}}}
4. There is an inconsistency in that the Integer method for power_mod is
called "powermod" instead of "power_mod". I think the Integer method
should be changed, for consistency with the naming conventions used
throughout sage (namely, be generous with underscores).
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/4850>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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