I too like find-new-spot but I once used a similar procedure and all was
well until it was used in a context in which every patch was occupied.
find-new-spot looped forever. At least move-to one-of patches with [not
any? turtles-here] reports a helpful error if there are no unoccupied
patches.
On the other hand while performance isn't an issue for the Segregation
Model that may not always be the case when move-to-unoccupied-patch is
called in other models. Note that move-to-unoccupied-patch should on
average be faster than find-new-spot when nearly all patches are occupied.
Another issue with find-new-spot is how to make a generic version where
turtles-here is not always appropriate. E.g. households-here might be
needed if there are other breeds of turtles on patches.
How about this?
to find-new-spot [satisfying-condition]
move-to one-of neighbors4
if not run satisfying-condition
[ find-new-spot]
end
to find-new-spot-without-any-turtles-here
find-new-spot task [not any? other turtles-here]
end
- ken kahn
On 30 December 2014 at 15:07, Seth Tisue <s...@tisue.net> wrote:
> Some thoughts about possible alternate versions of the Segregation
> model.
>
> In addition to considering how easily the code "reads" -- call it code
> simplicity -- I suggest also weighing computational simplicity.
> heavily. This sometimes aligns with code simplicity, but not always.
>
> NetLogo makes it really easy to write down something like `one-of
> patches with [not any? turtles-here]` without calling the coder's
> attention to the fact that running it always involves querying every
> patch in the entire world. This is problematic because it's slow,
> but you might also consider it conceptually problematic.
>
> I'm not saying it would be necessarily be wrong to decide in the end
> that exhaustive global search is a good thing to base a version of the
> model on. I just hope that the simplicity of the code involved isn't
> causing the issue to be glossed over.
>
> I would lean against anything involving `in-radius` because it's a
> circular neighborhood, which is both computationally expensive and a
> downright peculiar thing to be using at all in a grid-based model.
> (Imagine Thomas Schelling pulling out a compass and drawing circles on
> his checkerboard.) It's unfortunate that NetLogo doesn't have
> `in-von-neumann-radius` or `in-moore-radius`, so we end up reaching for
> `in-radius` just because it's there. (`von-neumann-distance` and
> `moore-distance` are missing as well.)
>
> Schelling writes of his 1D version, "rearrange the pluses and zeros by
> moving each dotted one to the nearest point where [...]". Another
> unfortunate gap in the NetLogo language is any simple way of expressing
> nearest-first search with early exit. One version of the model we've
> considered involves using `min-one-of`, but the resulting computation
> isn't done in nearest-first order, so more distant candidates are
> sometimes examined before nearer candidates, and it becomes necessary to
> limit the radius to prevent the search from becoming global. If NetLogo
> offered a concise way of expressing this kind of search, using it might
> result in my favorite version of all, but the language doesn't have it.
>
> None of my feelings about any of these choices are super strong, but
> personally, I like the random walk version:
>
> to find-new-spot
> move-to one-of neighbors4
> if any? other turtles-here
> [ find-new-spot]
> end
>
> I like it because it's strictly local, because it's dead simple, and
> because (like Schelling) it favors shorter moves. And it doesn't just
> happen to be dead simple when expressed in NetLogo's particular
> idiosyncratic vocabulary of primitives; it would be dead simple in any
> programming language, because it's dead simple conceptually.
>
> Note that I've used `neighbors4` rather than `neighbors`, since allowing
> diagonal moves is conceptually more complex and has an inconsistent
> distance metric (some moves are distance 1, others are distance
> 1.414...).
>
> If the use of recursion is considered obscure, consider rewriting as:
>
> to find-new-spot
> move-to one-of neighbors4
> while [any? other turtles-here] [
> move-to one-of neighbors4
> ]
> end
>
> Seth
>
> --
> You received this message because you are subscribed to the Google Groups
> "netlogo-devel" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to netlogo-devel+unsubscr...@googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.
>
--
You received this message because you are subscribed to the Google Groups
"netlogo-devel" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to netlogo-devel+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
