> Actually, I was kind of surprised that they were just lists of lists when I
> was looking at the code. Surely one wants more structure than that, or
> don't they have more structure? This is exactly the kind of thing we are
> just talking about with the game theory code - we want a class because you
> want to *do* something with it. Tab-completion rules! But I suppose it's
> possible that all these designs really are just lists of lists.
Yes, a combinatorial design is basically a set of subsets. The current
code of combinatorial design is intended to do lengthy computation for
constructing them. It is already a lot of time to run the code.
Involving some badly designed class would be at the moment the worse
thing to do. As an example
sage: timeit("for s in Subsets(range(5)): pass") # return Set
125 loops, best of 3: 3.97 ms per loop
sage: timeit("for s in subsets(range(5)): pass") # return list
625 loops, best of 3: 53.3 µs per loop
I am not saying that we do not need a proper class (note: there is
already IncidenceStructure). There are many things that one would like
to do with an orthogonal array:
- getting various graphs from it
- computing automorphism groups
- comparing isomorphism with another one
- looking for substructures
- etc
But right now, what Nathann is trying to do is rather orthogonal to
these questions. If somebody comes with a nice class that *does not*
slow down his construction code, everybody will be happy. Sage is open
to contributions and not only to critics ;-P
>> It is still largely possible to refactor the code, especially the
>> functions that are available from the global namespace. And it can be
>> done easily as it is just about modifying "design_catalog.py" which is
>> rather independent from the coming tickets.
>
>
>> For the internals, many constructions in combinatorial designs are
>> recursive and complicated. So separating the existence from
>> construction means do an exact copy of the code. The boolean answer is
>> just intended to cut the actual construction (the object are rather
>> big). So we can not live with two functions. On the other hand, this
>> function can be hidden from the global namespace.
>
> I guess I'm just surprised you need two functions; why can't you have one
> (underscore?) function that both of them call? That is what was surprising
> to me, if it really is an *exact* copy of the code?
more precisely:
{{{
if construction_X_is_possible(k,n):
if existence: return True
else: return build_the_design_with_X(k,n) # long time
}}}
But see Volker proposal about a function which returns None or functions as in
{{{
if construction_X_is_possible(k,n):
return build_the_design_with_X
}}}
> Thanks both Nathann and Vincent for explaining some of the more technical
> details.
Thanks for having a look into this.
Vincent
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