#5242: [with patch, needs review] generic_power can now handle semi-groups
---------------------------+------------------------------------------------
Reporter: hivert | Owner: tbd
Type: enhancement | Status: new
Priority: major | Milestone: sage-combinat
Component: algebra | Resolution:
Keywords: generic power |
---------------------------+------------------------------------------------
Old description:
> 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.
New description:
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 responsibility of raising an error when the
exponent n is negative and a is not invertible. This allows for monoids
with partially 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 revealed 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#comment:2>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To post to this group, send email to [email protected]
To unsubscribe from this group, send email to
[email protected]
For more options, visit this group at
http://groups.google.com/group/sage-trac?hl=en
-~----------~----~----~----~------~----~------~--~---
