Hi Christian,
2014-05-28 11:32 UTC+02:00, Christian Stump <christian.st...@gmail.com>:
>> It seems that actually nobody read my initial post on that thread... so
>> let me repeat
>
> I did -- but didn't really have any qualified contribution...
>
>> But the semantic has to be implemented at the level of maps not at the
>> level of methods.
>
> could you explain what you mean there (maybe using your example of the
> number of descents of a permutation).
A method ( = a Python function) is not a Sage Map ( = a Python object
that model a mathematical function). I would like first to convert the
method into a map
{{{
from sage.categories.map import Map
class NumberOfDescents(Map):
def __init__(self):
Map.__init__(Permutations(), NonNegativeIntegers())
def _call_(self, p):
return Integer(p.number_of_descents())
}}}
The above example is already non-trivial since it specifies a domain
and a codomain (which is different from the parent of the image of an
element):
{{{
sage: nod = NumberOfDescents()
sage: p = Permutation([3,2,1])
sage: nod(p)
3
sage: nod(p).parent() is NN
False
}}}
The second step would be to think how to add semantic to the map. Part
of is already managed by the axioms/categories (for example a Morphism
between GradedSets preserve the grading). But there is nothing for
injectivity/surjectivity or more subtle properties.
It would make more sense to register actual maps as above.
Vincent
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