#5242: [with patch, needs review] generic_power can now handle semi-groups
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Reporter: hivert | Owner: tbd
Type: enhancement | Status: new
Priority: major | Milestone:
Component: algebra | Keywords: generic power
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The former implementation of generic_power_c made two assumptions
- {{{not a}}} is well defined for any element a
- There is a one
These two assumptions do not always always hold. So I reorganized the
initial code which handle particular cases so that:
- it does not call "not a" when the exponent n is different from zero
- it delegates to ~a the responsability of raising an error when the
exponent n is negative and a is not invertible. This allows for monoids
with partialy defined inversion (e.g. the multiplicative monoid of Z/12Z).
This modification revealed a problem in matrices: the empty matrix 0x0
modulo 2 was tested to be non invertible! I changed the test to the
correct value.
Investigating this revealled many other inconsistencies with matrices;
those will
be taken care of in a subsequent patch.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5242>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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