2009/12/29 Nathann Cohen <nathann.co...@gmail.com>:
> Excellent ! Then
>
> __builtin__.sum([g,h],Graph())
>
> does the job.. Thank you :-)
>
> Nathann
>
This also works with out the __builtin__., in which case sum is
synonymous to sage.misc.functional.symbolic_sum which (at least in
this case) calls the builtin version.
sage: g = graphs.PetersenGraph()
sage: h = graphs.PetersenGraph()
sage: sum([g,h],Graph())
disjoint_union Petersen graph disjoint_union Petersen graph: Graph on
20 vertices
I wonder if, for a type which implements the call method in such a way
that 0 get coerces automatically to the zero object of the type (with
respect to sum), then it would not be necessary to add the extra
parameter Graph()? For example, this works:
sage: sum([g,h],type(g)())
disjoint_union Petersen graph disjoint_union Petersen graph: Graph on
20 vertices
and there must be other situations where the same would work; another
possibility is shown by this example:
sage: P,Q = EllipticCurve('389a1').gens()
sage: sum([P,Q])
(4 : 8 : 1)
which works because Sage knows how to coerce the integer 0 to the 0
point on an elliptic curve.
John
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