Just as an update and a follow up note on the cyclist/sperm aggregations, I've
developed (and am continuing to develop) a simple computer peloton simulation
and am working through a series of experiments. Aspects of the simulation apply
to certain sperm aggregates as well (at least I will suggest this).
The plan at this point if for the the sim to involve these sets of experiments:
1. a "no drafting" set where two or more sets of agents proceed according to
their own intrinsic max sustainable speed with no capacity to match the speed
of agents of other sets;
2. a "weak drafting" set, where weaker agents can match the speeds of others if
in a certain proximity of faster agents;
3. a "strong" drafting set where agents actually seek to match speeds of others
by following behind others.
I've completed a set of experiments for number 1, which is the obvious case in
which group sorting occurs according to maximum sustainable output, and the
easiest to simulate. The others are still underway.
My aim is to demonstrate that:
a. group sorting does in fact occur according to relative differences in power
output, and that aggregates occur because their effective fitness levels are
narrowed by a "drafting" effect so their speeds are identical;
b. there is a correlation between aggregate size (ie. number of agents),
differences in relative maximum sustainable output, and the time to which group
sorting occurs.
The prediction is that the time required for group sorting to occur increases
as aggregate size increases and relative differences in max output capacities
("fitness") become smaller. In other words where agents are identically fit,
they will all stay in one group and will never sort (generally); where fitness
levels are different, they will sort rapidly. Drafting facilitates the
narrowing of fitness levels, so even if there are intrinsic differences in
output, agents will aggregate if they can draft such that they travel at the
same speed and at effectively identical output levels.
At the moment, I have in mind that sperm aggregates fall under the category of
"weak" drafting, whereby they randomly/accidently draft, but are incapable of
seeking out drafting positions as are agents in bicycle pelotons. Pelotons
exhibit strong drafting. So, under a weak drafting model, sperm sorting should
occur at some rate faster than pelotons. In a peloton, especially one in which
the entire group consists of riders of closely matched sustainable outputs
(such as a group of professional cyclists), the group will stay together to the
finish (on a uniform course). In a peloton, the primary cause of group sorting
is the occurrence of points in which drafting benefit is reduced such that
drafting no longer equalizes the entire range of output levels, such as hills,
course obstacles, and cross-winds (I have refered in the past to these as
instabilities in the system). The nature of the proximity of sperm to one
another may mean that their weak drafting results in very long sort times, such
that sort times are nearly the same as would occur under a strong drafting
situation, and that is something I can look for as well. There may be some
surprises along the way.
If I can complete the experiments, I may seek to get the results published, or
I may aim to present them first at the 2010 AAAI Conference and seek
publication afterward. Basically the idea is to establish a model by which
predictions can be made for real aggregations, and the model should be
applicable essentially to all aggregates which move at maximum sustainable
outputs and where there is some energy saving component involved in coupled
motion. It won't apply where aggregates move at outputs significantly below max
sustainable outputs, because in those situations even the weakest agent can
keep up with the strongest (the extreme situation is where they all stand
still, or move at the equivalent of a slow walking pace). It can apply,
however, in situations where there is broad range of fitness levels and only
some agents move at maximum sustainable output, because a small increase in
output among the group causes those already at max output to be sorted "off the
back", even when many among the group are not at max output.
Vladimyr - sorry I haven't responded yet on a couple of your posts - I've
realized I need to knuckle down and really work through a simulation, and have
become focussed on that at this point. I hope to be involved in this
discussion more, however, over time.
Hugh
----- Original Message -----
From: Vladimyr Ivan Burachynsky
To: 'The Friday Morning Applied Complexity Coffee Group'
Sent: Saturday, April 10, 2010 10:16 AM
Subject: Re: [FRIAM] leadership in flocks
How similar to the sperm peloton and the cyclist peloton, now we have flocks
with leaders and cliques?.
If each model has a different organizing principle then why does my simple
mind think there are similarities?
I liked Hugh Trenchard's ideas the best, there was no need for more than a
simple available power assessment on the part of the individual agent. Sticking
the term leadership into the discussion really puts a strange twist to
everything.
Trenchard's ideas would have probably worked for the flocks equally well, and
that is truly interesting. Craig Reynolds 1982? wrote his early "Boids " paper
with only very simple principles none of which included power or aerodynamics.
Same organized behavior but completely different principles. Do we force
complex interpretations where simple ones suffice.
A "leader" in a cycling peloton is such a temporary phenomenon that one has
to be very careful how the term it is used. But in the bird flock the leader
seems to be part of a social dynamic which might not actual exist but in the
minds of the writers?
Inventing complex explanations for simple situations seems similar to what
conspiracy theorists practice.
Dr.Vladimyr Ivan Burachynsky
Ph.D.(Civil Eng.), M.Sc.(Mech.Eng.), M.Sc.(Biology)
120-1053 Beaverhill Blvd.
Winnipeg, Manitoba
CANADA R2J 3R2
(204) 2548321 Phone/Fax
[email protected]
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Ted Carmichael
Sent: April 10, 2010 5:39 AM
To: The Friday Morning Applied Complexity Coffee Group
Subject: Re: [FRIAM] leadership in flocks
I haven't read the papers all the way through, but on first blush, I don't
see them as contradictory. Either could be correct.
A "leader" - whether bird or person - could act first due to internal traits
(inclination, ability, imagination) or external influence. The first implies
that the leader is different from the others in some way, while the second
implies only a situational difference: circumstance rather than inherent traits.
Once the leader acts, this creates space for the other birds/people to act
similarly, and follow the leader. The followers must have had the same
inclination towards this action, because they end up doing it, too ... they
just weren't over the tipping point yet. There was something missing that kept
them from acting first. The leader's action clearly provides the missing
element, and so all the followers perform the same action.
The remarkable thing about the flocking models, such as the one in JASS, is
that they show that leadership doesn't have to be due to an internal trait. It
may simply be a situational difference among very similar agents. Before these
models were put forth, the prevailing view was that leadership is always
endogenous to the leader. Now, at least, we can consider other possibilities,
whether or not they end up being correct.
-t
On Fri, Apr 9, 2010 at 8:57 PM, glen e. p. ropella
<[email protected]> wrote:
sarbajit roy wrote circa 10-04-09 06:34 AM:
> The religious grouping I belong to had cause to study/discuss this about 150
> years back (concerning flocks of men not birds). The leader of the faction
> in opposition to mine (which means my faction vehemently disagrees with his
> view) had this to say
That quote from your opposition seems to fall in line with the nature
article, the idea that particular birds/humans (presumably with
particular traits, inbred or learned) turn out to be leaders. I take it
from your statement that you agree more with the jasss article, that
leaders with no particularly exceptional traits emerge? Right?
Of course, to even have this discussion, we have to allow ourselves the
metaphor between human cliques and bird flocks...
--
glen e. p. ropella, 971-222-9095, http://agent-based-modeling.com
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Meets Fridays 9a-11:30 at cafe at St. John's College
lectures, archives, unsubscribe, maps at http://www.friam.org
