Posted by
Phil Henshaw-2 on
Mar 30, 2008; 2:55pm
URL: http://friam.383.s1.nabble.com/Wed-Blender-Stereo-and-Computational-Photography-Videography-for-Cultural-Preservation-tp525972p525992.html
Hugh,
Yes, that example of the breaking point of the peloton does sound like the
limit of negotiated cooperation for the individual cyclists. Here everyone
expects the usefulness of the peloton to be abandoned entirely at some
point, and choosing just when to break from it is probably a critical
individual decision. It's an expected 'line of conflict' determined by when
the individual riders break free from the shelter of the group.
Here the common resource is the relative air-pocket formed by the group, and
the regularity of alternating positions within it. Maybe that would be
analogous to users sharing a bus and having negotiated some regular habit of
coordinating their uses of it. An established pattern of sharing is one of
the kinds of independent natural systems I focus on. Once established some
change could cause it to fall apart and then need to be completely
re-negotiated.
The canonical example is of a resource that begins with having no limit for
a small community of users with various cooperative habits for exploiting
it. If their habits constitute a growth system, the users will usually know
only their own individual experience and have no experiential information
about the approach of that limit. It's not clear what their best source of
information would be about it, or how they would choose what to do at the
limits.
What kind of information might indicate the approach of common resource
limits? How would that be different from evidence that other users are
breaking their agreements? As independent users of natural resources tend
to have less information about, or interest in, each other's particular
needs than, say, cyclists in a peloton, how would they begin to renegotiate
their common habits when circumstances require it?
Phil
-----Original Message-----
From: Hugh Trenchard [mailto:
[hidden email]]
Sent: Saturday, March 29, 2008 6:09 PM
To: sy at synapse9.com; The Friday Morning Applied Complexity Coffee Group
Subject: Re: [FRIAM] can you have 4 operating systems on one buss?
I might as well throw this example into the fray, which may cover a few of
your bases, Phil, though I'll happily stand corrected if they are not on
target.
The only complex system I can claim any sort of
slightly-more-than-superficial understanding is that of bicycle pelotons.
As I've mentioned in previous posts, a bicycle peloton is a group of
cyclists who ride within drafting range of each other (except for the riders
facing the wind), who thereby reduce their energy output by drafting. A
peloton is a very good example of resource optimization, since it easily
demonstrated that a peloton can travel faster and farther than an individual
cyclist on his or her own.
In high-level bicycle races, the range between the riders' ability is fairly
narrow (I've compiled some figures which show the range to be about 17
percent). The range is narrowed further by drafting, and I've also compiled
figures which show that the range is narrowed to an average of about 4%
between first and last place finishers in pelotons (as compared to 17%
between first and last place finishers in individual time trials, which is
where the first figure of 17% above comes from), and there are frequent race
situations where an entire peloton finishes with the same finishing time.
In any event, if I understand your original inquiry, a peloton is a good
example of the kinds of self-organized resource sharing you are talking
about. When cyclists set off at the beginning of a race, there is a period
when the speeds are low enough when they have no need to draft one another
to feel comfortable in any position in the peloton and are not expending
energy close to maximum capacity. However, as speeds increase, a transition
occurs (I argue this is a true phase transition) whereby resource sharing
becomes necessary as cyclists are either in drafting positions or at the
front (most are drafting).
In this phase, a balancing occurs between energy expenditure and optimal
position within the peloton. Because it is a competitive situation, it is
better to be positioned as close to the front as possible. As this is a
continuous imperative, rotational movements occur within the peloton, where
riders are moving up and down the peloton, or are caught in "eddies" whereby
they advance for relatively short distances within the peloton, before begin
shifted backward again, and then attempt to move forward again. These
movements occur while riders attempt to use as little energy as possible to
advance. So, where there are riders who shift to the outside of the pack
(facing the wind by doing so), other riders will follow in their draft.
This results in a pattern whereby riders advance up the sides for relatively
long stretches, while riders drop back within the peloton, and while within
the peloton there are these smaller-scale eddies.
Another phase transition occurs when the pace shifts up beyond another
threshold, whereby the speeds are too high for there to be continuous
rotational movement within the peloton, and the peloton stretches into a
single line. This phase, while easily observable, is a precurser to a final
transition where the peloton begins to splinter: individual riders fall off
the back, or separations occur in the line of riders which following riders
cannot bridge, and the peloton splinters.
This last phase is an example of the transition to "conflict" which you were
referring to, if I understand it correctly. In this situation, every rider
is either in direct competition with the each other, or small groups form
which cooperate internally, but each of which are also in direct conflict as
chasing groups want to reintegrate groups ahead, while groups ahead want to
stay ahead of those behind.
Does this sound a bit like the kind of resource sharing states you were
talking about?
Hugh Trenchard
----- Original Message -----
From: "Phil Henshaw" <
[hidden email]>
To: "'The Friday Morning Applied Complexity Coffee Group'"
<friam at redfish.com>
Cc: "'Diegert, Carl F'" <diegert at sandia.gov>
Sent: Saturday, March 29, 2008 9:02 AM
Subject: Re: [FRIAM] can you have 4 operating systems on one buss?
> Marcus,
> I think the boundary conditions of the problem include both the variable
> of
> system design and control, and that of the independent behaviors of the
> users. The question is what each of those contributes. With computer
> networks you can't do without both, of course, but you can consider what
> the
> options are for each independent of the other. Then both may learn to
> make
> a combined system work better.
>
> You say " ...resources can be managed by a secure executive process that
> divides up the work fairly. Systems that don't do this are non-critical
> systems." That is generally true for computer networks. Playing God
> and
> deciding what is fair is the practical thing in that circumstance, since
> the
> system emerged as a controlled system to start with.
>
> The network manager might be really 'out to lunch' some times though, and
> the users needed to share the resource without that global view and
> central
> control. What could they accomplish just between themselves, is the
> question. They'd have virtually none of the information the manager uses
> and none of the control. If left to themselves, how would they do it?
>
> I think they'd develop usage signals of various kinds, that communicate
> things like 'here I come' or 'now I'm done'. That would help optimize the
> use of the resource without making the users talk to each other to figure
> out and mesh each other's needs. There are signals that convey these
> kinds
> of messages in natural systems, like usage growth and decay patterns,
> which
> telegraph what will follow in considerable detail if you look into the
> derivative rates. That forecasting ability then allows responses before
> conflict arises. If users did that then everyone could get more out of
> the
> shared resource without dropping chains from overloading the buffers, or
> having to talk to each other.
>
> To me there are several things here that are closely analogous to the
> problem of optimizing the interaction between users of less well defined
> resources. For independent users of resources in open environments
> there's
> no 'God' person worth their salt as controller. Not knowing how to do
> without that role seems to have become a primary problem for the economies
> and all our complex shared uses of the earth in general.
>
> Does that make sense?
>
> Phil
>
>> sy at synapse9.com wrote:
>> > Now that since nearly anyone's taking of more resources is
>> increasingly robbing and disrupting other users, has sort of become the
>> main source of conflict on earth..
>> >
>> If someone wants to copy a real big amount of stuff from one node of a
>> cluster to another (there can be tens or thousands of these nodes), the
>> switch can connect these two nodes. All other transfers in the system
>> can be going on without notice of this. To the extent other people
>> want to deal with those two nodes, the switch can fairly divide down the
>> bandwidth between those people. This will typically be a small
>> fraction of the total capacity of the system or the network.
>> Furthermore, on a typical large cluster, there will be a parallel
>> filesystem with many independent block devices and very low latency
>> switches. If I have 100 nodes all writing at once to 100 different
>> block devices and there is a effectively a different wire from the node
>> to the drive, then there is no contention.
>>
>> If a hundred users all want to do this, with their respective
>> entitlements, and from different nodes, then at some point you run out
>> of gas. But a hundred users rarely if ever all want to do this.
>> This is a pretty standard assumption of many kinds of telecommunication
>> systems.
>>
>> So, neither wire networking nor bus use is usable for your analogy.
>> The reason is that these resources can be managed by a secure executive
>> process that divides up the work fairly. Systems that don't do this
>> are non-critical systems.
>
> [ph]
>
>>
>> Marcus
>>
>>
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>
>
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