Nathann,
> I understood from your explanation why Mod(1,n) is considered
> different from 0, and it is to me the correct behaviour... But what
> about this
>
> g has 21 vertices
> len(g.vertices) == 20 ?
>
> Sorry if you answered already ! :-)
I think the information was there, but I was not very clear. It is
better if you just look at the code:
{{{
cdef int get_vertex(object u, dict vertex_ints, dict vertex_labels,
CGraph G) except ? -2:
if u in vertex_ints:
return vertex_ints[u]
if (not isinstance(u, (int, long, Integer)) or
u < 0 or u >= G.active_vertices.size or
u in vertex_labels):
return -1
return u
}}}
When int(0) is input, it returns 0. When Mod(0, 20) is input, however,
it returns -1, meaning that the object is not yet in the translation
dictionaries (since the second block only tests for three types of
integer). So when int(0) is input to check_vertex(), nothing gets
added to the dictionaries. However, when Mod(0, 20) is input, it does
add an entry to the dicts, and since 0 is already taken up (as defined
in a bitset of which ones are used), it gets a different int. This is
how we get two zeros in the vertex dicts.
It is not clear to me how to solve this problem. One could add
IntegerMod to the list of types to check, but that's a slippery
slope... One very silly option is to simply make the behavior of
adding Python ints and IntegerMods at the same time undefined, but
there *must* be a better fix...
--
Robert L. Miller
http://www.rlmiller.org/
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