P ER H AGE
A further application of matrix analysis to communication structure in oceanic anthropology
Mathématiques et sciences humaines, tome 65 (1979), p. 51-69
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A FURTHER APPLICATION OF MATRIX ANALYSIS TO COMMUNICATION STRUCTURE IN OCEANIC ANTHROPOLOGY
PER
HAGE1
Prof. Yves Lemaitre
(1970).shows
how the matrixoperations
of theproduct (AA),
Boolean addition(1+1=1),
the transpose(At)
and elementwisemultiplication (A
xB)
may be used to findequivalence
classes in acommunication network. Lemaitre’s
proposal
amounts to anindependent
invention of certain aspects of
graph theory. Thus,
his matrices A andSn correspond
to theadjacency
andreachability
matrices A andRn
of agraph
ordigraph
and hisfigure
on page 104 whichjoins
theequivalence
classes found from S x
St (which "en quelque
sorts’debrouille’
lesrelations") corresponds
to the condensation of adigraph
into its strongcomponents
(Harary,
Norman andCartwright 1965).
Lemaitre’s example
is a directedgraph
of traditional inter-islandvoyaging
in Oceania where the matrix A shows one-step connections betweenpairs
of islands iand j,
the matrix S showsmultiple
step connections between iand j
and the matrix S xSt
shows(in its rows)
the maximalsubgraphs
ofmutually
reachable islands. The condenseddigraph
which1
Department
ofAnthropology, University
of Utahconsists of these
subgraphs
and theiradjacency
relationsprovides
asimple
and clear model of the communication
possibilities
in the entire area.Lemaitrets proposal
is of arealsignificance given
the renewedinterest in the settlement of
Oceania,
e,g.,Levison,
Ward and Webb(1973), Finney (1976),
and ofmethodological significance given
theincreasing anthropological recognition
ofgraph theory
as ametalanguage
for theanalysis
ofmorphological properties
of socialnetworks,
e.g., Barnes(1969, 1972),
Mitchell(1969), Hage (1979).
His
analysis suggests
a furtheranthropological application,
alsofrom
Oceania,
in which matrixoperations
and theorems fromHarary (1959, 1969)
can be used to elucidate certaincyclic properties
in the undirectedgraph
of a communication structure. Theexample
chosen is an inter-household
exchange system
in a New Guineavillage degcribed
in Schwimmer(1973, 1974).
The matrices shown and’used in thisanalysis
werecomputed
with
"DIG:
aDIGraph
program for theanalysis
of socialnetworks" (Putnam
and
Hage n.d,),
AN INTER-HOUSEHOLD EXCHANGE SYSTEM
As Nadel
(1957),
Barnes(1969, 1972),
Mitchell(1969)
and others haveemphasized,
thesignificant
feature of netwurkanalysis
is its concernwith the relations between the relations. A network is more than the sum
of its
dyads
and itspatterning
is notreliably
revealedby
their numberor
density.
Thesignificance
ofpatterning
is well illustrated in E.Schwimmer’s (1973, 1974) analysis
of asystem
ofgift exchange
among the Orokaiva whichshows how
a set af relations which are limited in number combine in a certain way to create aglobal
structure which unites mostof the
participants.
Theanalysis
whichfollows generalizes
his observationon the
significance
of circuits orcycles
in a network.Schwimmer describes a system of
gift-giving
in aPapuan village consisting
of 22 households. Thegift
consists of cooked taro,presented by
women but conceived of asmediating
relations between households.It was my
impression
that those households which maintained the mostfrequent
informal association with one another werealso those who made each other the most
frequent
tarogifts.
These were the households who were
deeply dependent
on oneanother in
sentiment,
in economictasks,
inpolitical support.
They
would tend to side with one another invillage disputes.
Thus,
tarogifts
were a ritual statement in which one house-hold
expressed
its desire for close association with another(Schwimmer 1973:127-128).
An
ethnographically
unusual andimportant
feature ofSchwimmer’s analysis
is his definition of"significant
socialrelations"’
in terms of thefrequency
of taro transactions:In
Sivepe
the number ofexchange
partners maintainedby
ahousehold varies from three to
fourteen,
with an average of 8.5. The first(i.e.
mostfrequent)
partner is involved in anaverage of 38 per cent of all taro
transactions,
the secondpartner
in 24 per cent, the third in 12 per cent while the, other
partnerships
account foronly
26 per cent of all taro transactions. It is clear that the first and second partnersare in a very
privileged position
incomparison
with theothers
(Schwimmer 1973:129).
A
significant
andpervasive
aspect of social interaction in Orokaivagenerally
and in thisparticular
system is themaking
ofrequests
notonly
between
preferential
partners but also betweenwidely separated
householdsjoined by
a series ofmediating
links:The Orokaiva are wary of relations with persons with whom
they
are not intimate.
They
do not like to make evensimple requests
of such persons butprefer
to make the requestthrough
inter-mediaries who are intimate with both sides. In that case it is
possible,
if the request cannot be met, for both sides to pre- tend that it was never made. No hard words arespoken, nobody
is
overtly
humiliated. There is acustomary blank, expression-
less
style
which is usedby
intermediaries for thetransmitting
of
requests--symbolic
gestures ofneutrality.
The mediatoravoids the risk of
endangering
his own alliance while stillmaking
what effort he can tosatisfy
theparty seeking
the. benefit. If he is
successful,
thebeneficiary
is to someextent indebted to him
(Schwimmer 1974:232).
It appears that
mediating
chains may be of considerablelength:
The
procedure
followed is that A and B use one or more persons to mediate between them. In thesimplest
case, where A and Bare
separated by only
one link in thechain, they
share thesame intimate associate who can act as mediator. If
they
donot share an
intimate,
i.e. ifthey
areseparated by
two ormore links in the
chain,
an accommodation may be reachedthrough
a series of mediators who actvicariously
on behalfof the
principal parties (Schwimmer 1973:134).
Schwimmer’s graph analysis
shows two structural features of thesystem:
the"cluster,"
defined as "intimateone-degree
links between all themembers"
which wouldcorrespond
to a maximalcomplete subgraph
andthe
’’circuit,"
which unites householdsthrough intermediaries,
whichwould
correspond
to acycle
in agraph.
The circuit he notes"...
is close to whatgraph
theorists call a Hamilton circuit(Harary
and Ross1954;
Flament1968)
and would be consistent with an almost total absence ofstratification" (Schwimmer 1974:231).
Schwimmer enumerates two such circuits(cycles): ‘~The largest
circuit or near-circuit connects thegreat majority
ofhouseholds [19
of22]
of all clans and may thus be considereda
unifying principle
for thevillage
as a whole. The second much morestrongly constructed,
links 11 households of theJegase-Sorovoi clans,
but includes not a
single
Sehohousehold"(Schwimmer 1973:132).
While neither of these
cycles
isactually Hamiltonian,
thatis, they
are not
spanning cycles
or ones which passthrough
everypoint
of thegraph,
Schwimmer’s remarks about the association of suchcycles
with structuralunity
and a relative absence of stratification raise ageneral question
about thesignificance
ofcycles per
se ingraphs
of communication structure. While it is difficult to determine whether agraph
is Hamil-tonian, i.e.,
whether everypoint
lies on asingle, complete cycle
of Gsince there is no
unique
criterion for such agraph (Harary 1969),
it isrelatively
easy to determine whether everypair
ofpoints lies
on a commoncycle
of G. The latter condition is true of anycyclic
block which mayor may not be Hamiltonian. In many situations it may be useful and sufficient to
simply
know this. If G is acyclic
block than certain conclusions can be drawn about theintegrity,
the flow of information and thepolitical
character of thesystem
insofar as this character ismorphologically
determined.ARTICULATION POINTS AND BLOCKS
Every pair
ofpoints
lies on a commoncycle
of G if G is acyclic block,
that is if G has at least three
points,
is connected and contains noarticulation
points (points
whose removal disconnects agraph
or component of agraph).
Theseproperties
aregiven by
theadjacency, reachability
and distance matrices of a
graph, A(G), R(G)
andN(G).
Figure
1 shows theadjacency
matrix of thegraph
G of the taro ex-change
system. It was constructed from TableVI/2
in Schwimmer(1973)
which
gives
thepreferential
partners of eachhousehold, by symmetrizing
the directed
graph
of the first and secondchoices (i.e.,
iand j
areadjacent
if either is a first or second partner of the other:(A
+A t
(This
would appear to beempirically justified
since no distinctions aremade as to the direction of the
gift
relation and since in all cases ex-cept
one, if ichooses j
as a first or second partner,then j
chooses iat least as a third
partner.) Figures
2 and 3 show thereachability
anddistance matrices constructed
using
thefollowing
theorems fromHarary,
Norman and
Cartwright’s
Structural models(1965)
fordigraphs
which alsoapply
tographs. (The
matricesR(G)
andN(G)
arepartitioned
to show thecomponents
of G--the maximal connectedsubgraphs):
THEOREM 5.7. For every
positive integer
n,COROLLARY 5.7a
(Harary
et al.1965:122)
THEOREM 5.19. Let
N (D). - d ..
be the distance matrix of _ija
given digraph
D.Then,
1.
Every
- -diagonal
entr ,dii
is0,
11
2. if
r.. = 0,
andij
>
3.
Otherwise,
ijd..
is the smallest power . n to which Amust be raised so that
> 0,
thatis,
so that2.L
the
i, j entry of
is 1.(Harary
et al.1965:135).
Figure
1.Adjacency
matrixA(G)
of the taroexchange
systemFigure
2.Reachability
matrixR(G)
of the taroexchange
systemFigure
3. Distance matrixN(G)
of the taroexchange
systemG has 22
points
and contains two components,c2
which consists of households8, 9,
10 andcl
which consists of theremaining
19.C2
isobviously
ablock;
the status ofcl
can be determinedby checking
forarticulation or cut
points using
two theorems inHarary (1959)
onN(G)
and then the delete
point provision
of DIG..The first theorem is based on the concept of the relative
peripher- ality
of thepoints
in agraph:
The associated number of a
point
of a connectedgraph
is thegreatest distance
between
thispoint
and all otherpoints.
Aperipheral point
... is apoint
whose associated number is maximal. Apoint
c isrelatively peripheral
frompoint
b ifthe distance between b and c is
equal
to the associated number of b. We are now able to state two sufficient con-ditions,
one of which assures us that apoint
is not a cutpoint
and the other that it is.THEOREM: All
relatively peripheral points
are not cutpoints.
(Harary 1959:390).
In the distance matrix of a
graph
therelatively peripheral points
are those with the
largest
number in each row. InN(cl) points 1, 6, 7, 11, 12, 13, 14, 15, 16, 18, 19, 20, 21,
22 are not articulationpoints.
The second theorem is based on the concept of a
point
at aunique
distance from anotherpoint:
THEOREM: If b is a
point
of a connectedgraph
and c is theonly point
at a certain distance from b less than the associ- ated number ofb,
then c is a cutpoint (Harary 1959:390).
N(G)
reveals no suchpoint
incl,, i.e.,
no rows in which there isa
unique
occurrence of a number less than the associated number of P.The status of the
remaining points
can be determinedby deleting
andthen
restoring
each one andnoting
in each case whether or notR(G)
remainsuniversal. The
result for c1is
that none of theremaining points
are articulationpoints,
soc1
is a block.To say that a connected
graph
of three or morepoints
has no articu-lation
points
isequivalent
tosaying
that everypair
ofpoints
lies ona common
cycle.
Thefollowing
theorem fromHarary (1969:27-28) gives
thefull
implications
of this statement andthereby
the conclusions which may be drawn about the structure ofcI’ (The analysis
is based on theexample
fordigraphs
inHarary
et al.1965:249-250.)
THEOREM 3.3. Let G be a connected
graph with
at leastthree
points. The following statements
areequivalent:
( 1)
G is a block.(2) Every
twopoints
of G lie on a commoncycle.
(3) Every point
and line of G lie on a commoncycle.
(4) Every
two lines of G lie on a commoncycle.
(5)
Given twopoints
and one line ofG, there
is apath joining the points
which contains the line.(6)
For every three distinctpoints
ofG,
there is apath
joining
any two of them which contains the third.(7) For
every three distinctpoints
ofG,
there is apath joining
any two of them which does not contain the third.(Harary 1969:27-28)
The
application
of Theorem 3.3 reveals a number of structural prop- erties ofcl,
thelarge
group whichcomprises
all but three households in thevillage. By
condition(1)
there is no household whosedisappearance
or demise will
disrupt
communication within the group andby
condition(4)
if any one household loses or falls out with a
preferential partner
anytwo households will still be able to communicate. The
system
is thereforestructurally
invulnerable.By
condition(2)
everypair
of households has(at least)
two alternativepaths by
which to makerequests
of each other.Further, by
condition(5)
anyparticular
link may occur in a mediational chain between any two households andby conditions(6)
and(7)
any par- ticular household may occur in a chain but noparticular
household mustnecessarily
occur. The communication structure is therefore flexible in the alternative channels it allows. And it isegalitarian
or unstratifiedto the extent that relative power
depends
on theability
of any one household touniquely
control the flow of information between any two households or sets of households.This
analysis
does not of course exhaust theempirically significant
features of the taro
exchange system. Thus,
certain households may commu-nicate more
frequently,
moreeffectively
and so on. But it does serveto
operationalize
concepts such as’’egalitarian,"
"flexible" and "in-vulnerable."
It reveals certainglobal properties
of thesystem
andthereby
defines the constraints within which actual communication mustoperate.
Two further
general
observations may be made on theempirical significance
of block structures in socialorganization.
1. Blocks and group size. In a
complete graph kp
which hasp(p-l)/2
relations the communication structure is invulnerable and flexible. If
a group
expands
in size while the number of relations remains the same or does not increasecommensurately (assuming
some limitation on thequantity
of energy, e.g. tarogifts,
at thedisposal
of each unit tocommunicate)
theseproperties
may still bepreserved
if the structureremains a
block,
which may have as few as p relations. All that is re-quired
is the addition of a limited number of new relationsstrategically
placed and/or
the redistribution of someprevious
relations. A block is aminimal
means for the creation of alarge
cohesive structure.2. Blocks and norm enforcement. In a block there is
provision
forflexible
communication since A may use eitherpath
1 orpath
2 in communi-cating
with B and also for redundant communication since A may useboth paths
I and 2 to transmit the same message to B. Mitchell has observedthat,
#if.
The
sociological significance
of the notion ofreachability
lies in the way in which the links in a
person’s
networkmay be channels for the transmission of information
including judgements
andopinions especially
when these serve to re-inforce norms and
bring
pressure to bear[on]
somespecified
person
(Mitchell 1969:17).
In blocks such pressure may be
multiplied by
the transmission of the samemessage which arrives at a person
through multiple
channels(as exemplified
in one
meaning
of theexpression,
"’he wasgetting
it from allsides").
DISCUSSION AND GENERALIZATION
The
preceding analysis
shows how matrixoperations
and theorems fromgraph theory
may be used to elucidate the communication structure of a group, withparticular
reference to blocks in undirectedgraphs.
Relatedpotential anthropological applications
are contained in thefollowing
concepts and references.Clusters in
signed graphs
A
signed graph
S is one in which the lines havepositive
ornegative
valueswhich represent antithetical relations. An illustration comes from the data in M.
Young’s (1971) monograph
which describes a system ofcompetitive
foodexchange
onGoodenough
Island in Melanesia. The system consists of ninepatrilineal
clans or clan segments each of which has traditional foodfriends, fofofo,
and foodenemies,
nibai. Nibai makecompetitive gifts
of
food, niune,
to each other(which
therecipients
do not consume butpass on to their
respective fofofo).
In confrontations between groups, those connecteddirectly
andindirectly by
fofofo links support each other. Thesystem
may berepresented by
thes-graph
inFigure
4 in whichpositive (fofofo)
relations are shownby
solid lines andnegative (nibai)
relations
by
broken lines.Figure
4. Asigned graph
S of inter-clancompetitive
foodexchange
in KalaunaAn
empirical prediction
about structuresconsisting
of antithetical relations is thatthey
will contain clusters such that allpositive
re-lations
join
units withinsubgroups (clusters)
and allnegative
relationsjoin
units in differentsubgroups (Davis 1967). Figure
4 forexample
contains three clusters
(S,,
.s
29’3 S3).
If the structure of a group isclusterable,
there is no contradiction such that an enemy of a friend is a friend(or
such that a friend of a friend is an enemy or that a friend of an enemy is afriend). (If
a group ispolarized
into twoclusters then it is also true that an enemy of an enemy is not an
enemy.)
Such structures are
presumably
stable and it issignificant
thatYoung
describes the clanalignments
ascorresponding
to a"general
balance ofpower."
One criterion for a clusterables-graph
is in terms of thecycles
of agraph:
THEOREM 1. Let S
by
anysigned graph.
Then S has aclustering
if and
only
if S contains nocycle having exactly
onenegative
line
(Davis 1967:181).
Additionally
andequiva.lently,
because "S has nonegative
linejoining
two
points
in the samepositive component" (Cartwright
andHarary
1968:85,
Theorem1).
The
clustering
ofFigure
4 isapparent by inspection.
Forlarge s-graphs
Gleason andCartwright (1967)
have shown how matrixoperations
may be used to determine
(1)
whether S isclusterable, (2)
what itsclusters are and
(3)
whether theclustering
isunique. Also, Peay (1970) provides
a method fordetermining
whether there is astatistically
significant tendency
towardsclustering
in ans-graph.
These concepts and methods may have wideapplication
in Melanesianethnography
wheretribal structure often involves
traditionally
definedfriend/enemy
relations
existing
among alarge
number of groups(Strathern 1969,
Berndt
1964, Hage 1973).
We may note inpassing
thatRyan’s (1959) concept
of"clan cluster"
in the social structure of the Mendi inHighland
New Guinea wouldeasily
be treated as aspecial
case ofclusterability
ins-graphs--in
theexample Ryan gives,
ofunique
2-clustering.
Connectedness in directed
graphs
One matrix of
particular
interest withrespect
toLemaitre’s
method isthe connectedness matrix
C(D).
In Lemaitre theequivalence
classes are foundby
the elementwisemultiplication
of thereachability
matrix and,
its
transpose,
S xS .
A moregeneral matrix, given
inHarary
et al.(1965),
is the connectednessmatrix, C(D)
which is based on theparti- tioning
of D into its weak components and the addition of R andR’:
THEOREM 5.18. For any
digraph D,
the connectedness matrixC =[c..]
is obtained from thereachability
matrixR - r ..
ij
>as follows:
1. If
vi
and v. are in the same weak component,-
1
- --:l
..2.
Otherwise,
-2:l. -cij = 0 (Harary
et al.1965:133).
C(D) provides
thefollowing
information about the structural prop- erties of D based on the entries0, 1, 2,
3:(1)
the connectedness ofD, C 0 (disconnected), C 1 (weak), C 2 (unilateral), C 3 (strong)2 (given
by
the minimum entry0, 1, 2,
3 inC); (2)
the connectedness of everypair
ofpoints (given by
theentry
inc..);
1J(3)
the strongcomponents
of D
(given by
the entries of 3 in the rows ofC).
In theexample
ofinter-island
communication,
one would know from this matrix the reacha-bility
relation for both the entiredigraph
and for everypair
of islandsas well as the subsets of
mutually
reachable islands. Thismatrix,
in turn, could beexploited
togain
new information. Forexample,
thestructural
significance
of each island in the network of communication could be determinedby deleting
it andseeing
how its presence or absence affects the relation ofreachability
in the network(i.e.
the connected-2 D is weak if every
pair
ofpoints
isjoined by
asemipath,
unilateralif for every
pair
ofpoints
at least one can reach the other andstrong
if every twopoints
aremutually
reachable(Harary
et al.1965).
ness
category
ofD). (See
the discussion ofstrengthening, weakening
and neutral
points
inHarary
et al.1965:230-241.)
Path
strength in
valuedgraphs
A valued
graph
is one in which numerical values areassigned
to thelines,
which may represent thestrength
of a relation between apair
of
points.
Doreian(1974)
has shown how standard matrix methods may be modified to determine thestrength
of areachability
relation between everypair
ofpoints.
Thisprocedure might
be useful in a case such asSchwimmer’s
whichdistinguishes
thresholds of socialrelationships (first,
second and third
preferential partnerships)
or in one such as therecent
computer
simulation of drift voyages in Oceania(Levison,
Wardand Webb
1973)
which showsdigraphs
of inter-island contact similar to those in Lemaitreexcept
that the lines are drawn in different thick-nesses to show different
categories (from
two tofive)
of the likelihood of contact.CONCLUSION
This paper
provides
a furtherapplication
of Lemaitre’s matrix methods for theanalysis
ofequivalence
classes in an inter-island communication networkby showing how,
inconjunction
with a set of theorems fromHarary, they
may be used to elucidatecyclic
blocks in an inter-householdexchange system. Lemaitre’s
methods can be subsumed under the moregeneral
math-ematical
theory
ofgraphs.
Thistheory
contains additional matrices based on the sameoperations
anddistinguishes
differenttypes
ofgraphs --directed, undirected, signed
and valuedgraphs--each
of which may be coordinated toparticular
types of communication and social structuresfound in Oceanic
ethnography
andpresumably generally.
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