=Paper=
{{Paper
|id=Vol-1614/paper_21
|storemode=property
|title=Descriptive Models of System Dynamics
|pdfUrl=https://ceur-ws.org/Vol-1614/paper_21.pdf
|volume=Vol-1614
|authors=Grygoriy Zholtkevych,Konstantin Nosov,Yuri Bespalov,Larisa Rak,Elena Vysotskaya,Yulia Balkova,Vadim Kolomiychenko
|dblpUrl=https://dblp.org/rec/conf/icteri/ZholtkevychNBRV16
}}
==Descriptive Models of System Dynamics==
https://ceur-ws.org/Vol-1614/paper_21.pdf
Descriptive Models of System Dynamics
Zholtkevych G. N.1 , Nosov K. V.1 , Bespalov Yu. G.1 , Rak L. I.1 ,
Vysotskaya E. V.2 , Balkova Y. B.1 , and Kolomiychenko V. K.2
1
V. N. Karazin Kharkiv Nat. Univ.,
4, Svobody Sqr., Kharkiv, 61077, Ukraine
g.zholtkevych@gmail.com, k.nosov@yahoo.com
2
Kharkiv Nat. Univ. of Radio-Electronics
Science ave., 14, Kharkiv, 61166, Ukraine
Abstract. Nowadays in the course of investigation researchers are fac-
ing large arrays and datasets required fast processing, analysis and draw-
ing adequate conclusions. Data mining, statistical methods and big data
analytics provide an impressive arsenal of tools allowing scientists to
solve these tasks. However, investigators often require techniques that
enable with use of relatively simple and cheap measurements of easily
accessible parameters to build useful and meaningful concepts.
In our paper two classes of dynamical models aimed at revealing between-
component relationships in natural systems with feedback are presented.
The idea of both models follows from the frameworks of theoretical bi-
ology and ecology regarding pairwise interactions between the parts of
the system as background of system behavior. Both deterministic and
stochastic cases are considered, that allow us to determine the direction
of pairwise relationships in the deterministic case and the direction and
strength of relationships in the stochastic one.
Keywords: dynamical systems, deterministic models, stochastic mod-
els, Markov chains
Keyterms: Model, MathematicalModel, MathematicalModeling, Com-
puterSimulation
1 Introduction
The world of scientific research has been immersing into an extraordi-
nary information explosion over past decades, accompanied by the rapid
growth in the use of Internet and the number of connected computers
worldwide. We see a rate of increase in data growth that is faster than
at any period throughout history. Enterprise application and machine-
generated data continue to grow exponentially, challenging experts and
researchers to develop new innovative techniques to evaluate hardware
and software technologies and to develop new methods of big data inves-
tigation [1].
ICTERI 2016, Kyiv, Ukraine, June 21-24, 2016
Copyright © 2016 by the paper authors
- 58 -
Heterogeneity, scale, timeliness, complexity, and privacy problems with
big data impede at all phases of obtaining value from data. The problems
begin during data acquisition, when the amount of data requires us to
make decisions, currently in an ad hoc manner, about importance and
interpretability of data. Besides, much data today are not natively in
structured format, have gaps and incomplete. Hence, data analysis, or-
ganization, retrieval, and modeling are foundational challenges. Finally,
presentation of the results and its interpretation by non-technical domain
experts is crucial to extracting actionable knowledge.
Our study is devoted to the well-known problem of revealing condi-
tions of stability in natural systems providing long and steady develop-
ment and existence of systems. Today there is a large amount of online
big data collections comprising datasets taken from different branches of
biology, health sciences, ecology etc. As examples we can mention Data
Centre of International Council for the Exploration of the Sea (includes
hundreds of thousands marine biology related datasets), which were used
in the current investigation.
The problem of homeostasis and stability in the living organisms com-
munity or natural systems (biological or ecological) is closely related to
the problem of dynamic stability. The practical aspect of this problem is
connected to the disturbance in stability of systems, that is often accom-
panied, for example, by outbreaks in number or biomass of species.
The study of stability in communities or natural systems is closely
connected to investigation of relationships that determine the dynamic
characters of a system, i. e. relationships between systems parameters
having influence on the system dynamics.
For decades systemic methods, for example, based on the Shannon
index of diversity, have been used for studying the relationships between
the structure and stability of a system. Generalizing that and other ap-
proaches, Margalef [2] states that “the ecologist sees in any measure of
diversity an expression of the possibilities of constructing feedback sys-
tems, or any sort of links, in a given assemblage of species”. Similar ideas
were therefore presented in studying the structure of correlation pleiads,
in using cluster analysis and other statistical techniques to establish such
relationships for investigating similar problems.
Despite different approaches to revealing between-component relation-
ships, in biology and ecology there is a general approach in studying
such relationships, based on the following pairwise relationships: (+, +),
(−, −), (−, +), (−, 0), (+, 0), (0, 0). For the multi-component systems,
this set of relationships exhausts all possible pairwise inter-component
- 59 -
relationships categorized by the type of effect and have been studied at
length, particularly, in biology and ecology [3–5]. Therefor, in the cur-
rent paper the analysis of the relationships structure is based on the idea
of regarding the objects (i. e., living organisms in a community, species
etc.) as components of a system between which the pairwise relationships
mentioned above are possible. This allows us to present the structure of
relationships in an explicit form of relationships between the components
of a natural system.
It should be noted, that mentioned relationships not always can be
revealed with the help of statistical methods. For example, correlation
analysis is initially used for estimation of a relationship between two or
more variables, but it covers only statistical relation and cannot reveal a
cause-effect relationship [6].
There are statistical methods (structural relation modeling, analysis of
path and adjacent techniques), which are devoted to revealing between-
component relationships (and other tasks as latent variables’ analysis)
and can be used for casuality analysis [7, 8]. But these methods express
the relationships in a system in the terms of regression coefficients and
not in the form of paired relationships. Besides, interpretation of results
of this analysis is occasionally difficult (e.g. studying relationship between
a feedback system and homeostasis in a community).
2 Theory
Here we present two dynamical models developed for revealing between-
component relationships on the base of observation data obtained from a
real natural system.
First model has deterministic dynamic, finite number of states and
discrete time. As it is described in [9] at length, here we describe the
model in brief. The second model is stochastic and will be describe in
more detailed. Both models have a common background, so we begin with
its description and later will go to specific properties of each models.
We assume that a natural system to be modelled comprises N com-
ponents, which can be denoted by A1 , A2 , . . ., AN . It is assumed that the
component take integer values 1, 2, . . ., K, i. e. K value for each compo-
nent. The value 1 means a minimum amount of a component, the value
K means maximum, i. e. the component value varies from 1 to K.
The system develops in discrete time and the moments of time are to
be denoted t = 0, 1, . . .. So, the value of the component Ai at the moment
of time t = 0, 1, . . . are numbers Ai (0), Ai (1), . . ..
- 60 -
The next properties of a system are different for deterministic and
stochastic cases, so we shall describe them separately.
2.1 Deterministic model revealing the direction of
between-component relationships
We begin with deterministic case discussed, as mentioned, in [9] and was
named the Discrete model of dynamical systems with feedback. For the
deterministic system its state at the moment t + 1 is fully and definitively
determined by the state at the moment t.
If the system at the moment t is in the state (A1 (0), A2 (0), . . . , AN (0)),
all the following states can be written as the trajectory, where each column
is a state at corresponding moment:
A1 (0) A1 (1) A1 (2) . . .
A2 (0) A2 (1) A2 (2) . . .
. (1)
.. .. ..
. . . . ..
AN (0) AN (1) AN (2) . . .
In the theory of dynamical systems [10], such a system is called a
free dynamical system with discrete time. The system has only finite
number of states, so there exists a positive integer T , which can be called
a period of the trajectory, for which the conditions of periodicity hold
Ai (s) = Ai (s + T ) for enough large s.
Taking into account the periodicity, it is possible to extract the fol-
lowing minor form (1)
A1 (s) A1 (s + 1) . . . A1 (s + T − 1)
A2 (s) A2 (s + 1) . . . A2 (s + T − 1)
(2)
.. .. . . ..
. . . .
AN (s) AN (s + 1) . . . AN (s + T − 1)
presenting full description of the dynamics of the system.
Now we introduce the concept of relationships between components.
Let Ω = {−, 0, +}. A relationship between specified components Ai and
Aj is determined as an entry from the set Ω×Ω and denoted by Λ(Ai , Aj ) =
(ω1 , ω2 ), where ω1 ∈ Ω, ω2 ∈ Ω. If Λ(Ai , Aj ) = (ω1 , ω2 ), this means that:
- if ω1 = {−}, then large values of the Aj will lower the value of the
Ai .
- if ω1 = {0}, then the Aj doesn’t influence the value of the component
Ai .
- 61 -
- if ω1 = {+}, then large values of the Aj will raise the value of the
Ai .
The relationship Λ is antisymmetric in the following sense: Λ(Ai ,
Aj ) = (ω1 , ω2 ) implies Λ(Aj , Ai ) = (ω2 , ω1 ).
Assume that all the relationships Λ(Aj , Ai ) between all pairs (Aj , Ai )
of components A1 , A2 , . . ., AN are given. For each Aj and each (s, u) ∈
Ω × Ω it is possible to find the set of components, with which Aj has the
relationship (s, u)
Lj (s, u) = {Ai |Λ(Aj , Ai ) = (s, u)}.
Let κ = {1, 2, . . . , K} is to be the set of the states of an individual
component and Nj (s, u) is the number of components in the set Lj (s, u),
j = 1, 2, . . . , N , (s, u) ∈ Ω × Ω. A transition from the state at t to the
state at t + 1 is described by N transition functions Fj , each of which
defines the mapping
κ Nj (+,+)+Nj (+,0)+Nj (+,−)+Nj (−,+)+Nj (−,0)+Nj (−,−) 7→ κ.
Two types of relationships, intrinsic to natural systems. For more
detailed description of the dynamics of a natural system, one needs to
specify the explicit form of the transitional mapping. mino We intro-
duced two approaches based on the concepts of biological interactions:
weight functions’ approach and approach based on principles of Justus
von Liebich’s law.
Define the following functions on the set κ: Inc(A) = min{K, A + 1},
Dec(A) = max{1, A − 1}.
The system dynamics based on weight functions’ approach. First we define
the type of dynamics, which takes into account the weighted sum of all
Aj (t) (inclusive Ai (t)) for calculating the value of the component Ai at
the moment t + 1.
As we defined above, for each j (j = 1, 2, . . ., N ) and each pair
(s, u) ∈ Ω × Ω there exists the set Lj (s, u) with Nj (s, u) entries. Assume
hs,ui hs,ui hs,ui
that the function ϕj,1 (·), ϕj,2 (·), . . ., ϕj,Nj (s,u) (·) are to be the functions
of interactions of those components, with which the Aj has relationships
(s, u).
The functions are defined on the discrete set κ and have the following
h+,+i h+,0i h+,−i
properties: (i) ϕj,k (·), ϕj,k (·), ϕj,k (·) are increasing functions; (ii)
h−,+i h−,0i h−,−i hs,ui
ϕj,k (·), ϕj,k (·), ϕj,k (·) are decreasing functions; (iii) ϕj,k (1) = 0
for any (s, u) ∈ Ω × Ω.
- 62 -
We also introduce the numbers δj > 0 (j = 1, 2, . . . , N ) which can be
called thresholds of sensitivity.
For the system’s state at the moment of time t the following value is
calculated
P h+,+i P h+,0i
dj = Ak ∈Lj (+,+) ϕj,k (Ak (t)) + Ak ∈Lj (+,0) ϕj,k (Ak (t))+
P h+,−i P h−,+i
Ak ∈Lj (+,−) ϕj,k (Ak (t)) + Ak ∈Lj (−,+) ϕj,k (Ak (t))+ (3)
P h−,0i P h−,−i
Ak ∈Lj (−,0) ϕj,k (Ak (t)) + Ak ∈Lj (−,−) ϕj,k (Ak (t)).
The value of the component Aj is being changed according to the
value dj by the following rules
1. if dj ≥ δj , then Aj (t + 1) = Inc(Aj (t));
2. if dj ≤ −δj , then Aj (t + 1) = Dec(Aj (t));
3. if −δj < dj < δj , then Aj (t + 1) = Aj (t).
Now, the meaning of introduced transition functions can be explained
h−,+i
in clear way. For example, the functions ϕj,k (·) (k = 1, 2, . . . , Nj (−, +))
reflects the influence upon the component Aj of components in the set
Lj (−, +), which are related with Aj by relationship (−, +). The greater
the influence (i. e. the greater values of Ai (t) from the set Lj (−, +)), the
lower the values of dj .
The dynamics based on the Liebig’s law of the minimum. Next approach
is based on principles of Justus von Liebich’s law (Liebig’s law of the min-
imum) and essentially differs from the first approach, which is basically
additive.
Omitting the details, enough to say, that according to this approach,
transition from the state (A1 (t), A2 (t), . . . , An (t)) is defined by relations
of the state with two matrices C and C ∗ playing the role of a threshold.
The system identification with use of the observation data. While
dealing with real data, we often don’t observe the data in dynamics. Often
real data come unordered in time in contrast to data used for time series
modeling. So we don’t observe any dynamism described by the trajectory
(1) or the minor (2).
Usually, the result of observation is represented by a table of cases:
C11 C12 . . . C1B
C21 C22 . . . C2B
M̃ = . . , (4)
.. . .
.. . . ..
CN 1 CN 2 . . . CN B
- 63 -
where columns correspond to cases and rows correspond to components
(N components and B cases). We emphasize unordered character of the
data above, i. e. these is no time order between the cases in the table M̃ .
Here we describe a principle allowing to reveal the system relationships
of above mentioned type on the basis of the observation table M̃ .
This algorithm determines inter- and intra-component relationships,
which are as close as possible to relationships, which form matrix (2) in
some sense.
Assume that relationships structure is given. In that case for initial
state (A1 (0), A2 (0), . . ., AN (0)) and for given sets L1 (u, s), L2 (u, s), . . .,
LN (u, s), u ∈ Ω, s ∈ Ω the minor (2) can be calculated. Let P is to be
the correlation matrix (Pearson or Spearman) between the rows of the
minor (2) with entries ri,j . Also, for the table M̃ , the correlation matrix
P̃ (with entries ρi,j ) of its rows can be calculated.
Introduce the measure of distance between the matrices P and P̃
N
X −1 N
X
D(P, P̃ ) = (rij − ρij )2 . (5)
i=1 j=i+1
We state the task of minimization D(P, P̃ ) by all possible vectors of
initial states (A1 (0), A2 (0), . . ., AN (0)) and all allowable sets Lj (s, u),
s ∈ Ω, u ∈ Ω for all j
(by all initial states &
D(P, P̃ ) 7→ min (6)
by all allowable sets Lj (s, u)).
The stated task means the search for such relationships between com-
ponents, that the minor (2) is to be as close as possible to the table of
observations regarding the measure (5).
The following theorem proved in [9] shows that this task is well-
grounded in probabilistic sense.
Theorem 1. If the table of observations M̃ is obtained from the minor
(2) by equiprobable choice of columns, then the Pearson correlation matrix
of the observations table P̃ converges to the correlation matrix of minor
P (in probability)
lim ρij = rij , i = 1, 2, . . . , N, j = 1, 2, . . . , N.
B→∞
The same result takes place for the Spearman correlation matrix as
well.
- 64 -
2.2 Additive stochastic model of between-component
relationships
Our second model is also described by a set of components A1 , A2 , . . .,
AN taking discrete values 1, 2, . . ., K.
But, in contrast to the first one, the second model introduces into
consideration not only direction of relationships (in fact, for the first
model we considered three direction — negative, neutral, and positive),
but also a strength of relationships. Hence, relationships in this case can
be recognized besides directions by the strength.
The structure of relationships between components A1 , A2 , . . ., AN is
described by the following relationships matrix
m1,1 m1,2 . . . m1,N
m2,1 m2,2 . . . m2,N
M= . .. .
. .. . .
. . . .
mN,1 mN,2 . . . mN,N
Any entry mi,j reflects the strength and direction of influence of the
component Aj upon the component Ai . The direction of influence is ex-
pressed by the sign of the value mi,j (may be −, 0, +) and the strength
— by modulus of mi,j and varies from 0 to 1. So, −1 ≤ mi,j ≤ 1 for
each i, j. The influence of the component Ai on Aj is expressed by mj,i .
It is easy to see, that the relationship between the components Ai on Aj
is described by the pair (mi,j , mj,i ), which is close by implication to the
relationship (ω1 , ω2 ) introduced for the first model.
Now describe the dynamics of transition from the state of the sys-
tem at the moment t to the state at the next moment t + 1. As for the
weight functions’ approach, we assume, that a set of functions ψi,j (·), (
i, j = 1, 2, . . . , N ) reflecting relationships between all pairs of components,
including inner relationships, are given. The functions ψi,j (·) have the fol-
lowing properties: (i) ψi,j (·) are defined on the set κ; (ii) ψi,j (1) > 0; (iii)
ψi,j (·) are increasing functions on κ.
Also assume that a positive number δ playing the role of threshold, is
given. Let the system is to be in the state (A1 (t), A2 (t), . . . , AN (t)). For
each pair of indices define the random variable ξi,j as follows
sign(mi,j ) · ψi,j (Aj (t)) with probability |mi,j |,
ξi,j =
0 with probability 1 − |mi,j |.
N
P
Then we calculate the set of N random variables di = ξi,j , i =
j=1
1, 2, . . . , N.
- 65 -
Using the set (d1 , d2 , . . . , dN ), it’s possible to calculate the set of prob-
abilities (p− 0 +
i , pi , pi ) for each i according to the rule
p− 0 +
i = P (di ≥ δ), pi = P (−δ < di < δ), pi = P (di ≤ −δ)
for each i from 1 to N .
This definition implies the equality p− 0 +
i + pi + pi = 1. The transition
from the state at the moment t to the next state at t + 1 is defied by
following rule
−
Dec(Ai (t)) with probability pi ,
Ai (t + 1) = Ai (t) 0
with probability pi ,
Inc(Ai (t)) with probability p+
i .
That is, at the moment t + 1 the value of Ai can increase by 1, remain
the same or decrease by 1 with probabilities p− 0 +
i , pi , pi correspondingly.
Applying this rule for each i, the probabilities of transition from any
appropriate state (A1 (t), A2 (t), . . . , AN (t)) can be calculated.
It can be shown, that if each row of the matrix M include both neg-
ative and positive entries, we obtain the Markov chain with K N states
A1 (t), A2 (t), . . . , AN (t) (Ai ∈ κ). Besides, this chain is regular, so there
a unique steady-state stochastic vector w.
Now the reasons that state behind this model, can be explained. We
assume, that a natural system is described by this model, and the proba-
bility of staying the system in states converges to the entries of the vector
w. Using the states A1 A2 , . . . , AN and the components of the steady-
state vector w we can calculate a weighted Pearson correlation matrix
[11] between the components. Denote such the matrix by Rw .
We suppose, that the true dynamics of our natural system is not
visible, i. e. we cannot observe time series of states, but can record a
state of the system at random moments of time. These observations are
collected in the observation table M̃ having N variables and B cases
(after B observations) in similar way as for analogous table (4) of the
first model. Let the Pearson correlation matrix between rows of (4) is
denoted by R̃ .
Theorem 2. If the observation table M̃ is obtained according to the
way described above, we have
R̃ → Rw in probability when B → ∞.
This means component-wise convergence.
Proof. Omitted for short.
- 66 -
Introduce the measure of proximity for the matrices R and R̃
N
X −1 N
X
D(Rw , R̃) = (R̃i,j − [Rw ]i,j )2 . (7)
i=1 j=i+1
The result proved in the theorem 2 means that the sample observation
matrix consistently represents a true dynamics, not observed straightfor-
wardly. This result works as a base for identifications of entries of the
relationships matrix M. Therefore we can try to calculate transition prob-
abilities of the Markov chain, that provide the best approximation of a
true correlation matrix by a sample matrix in the sense of the measure
(7). So, M is obtained by resolving the following optimization task
D(Rw , R̃) 7→ min by entries mi,j .
In fact, we find the relationships matrix M, which makes the modelled
correlation matrix as close as possible to the observe correlation matrix.
3 Case Studies
We present here three examples from different areas, where our models
were applied.
First example concerns analysis of system factors affecting activity
of social networks users, playing an important role in modern culture
[12]. The structure of relationships between components of the system
for two states of the Internet-forum on fantasy literature were calcu-
lated and compared. This comparison aimed to reveal system aspects
of forum visiting in two periods. One state can be regarded as “low-
performance”, other as “high-performance” according to number of writ-
ten fanfictions (also abbreviated as fan fics, fanfics) of visitors at the site
dedicated to the cycle of novels of Joanne Rowling about Harry Potter
(snapetales.com). The period of first half of December 2010 is regarded as
“high-performance”, the second period of the first half of December 2014
is called “low-performance”. For these two periods a statistically signifi-
cant difference according to Student t-test (p < 0.05) in average number
of visits per day was also detected.
The fanfictions were divided into 4 categories according to their length:
fanfictions of small, large, and medium size; the last, fourth category in-
cludes fanfictions not related to the novels about Harry Potter.
The following values were taken as the components of the system
reflecting the authors activity
- 67 -
– the number of fanfictions of small size per day related to the cycle of
novels about Harry Potter (denoted by MIN);
– the number of similar fanfictions of large size per day (MAX);
– the number of similar fanfictions of medium size denoted by (MID);
– the number of fanfictions denoted by not related to the cycle of novels
about Harry Potter, based on another literary works (OTHER).
For the “high-performance” and “low-performance” periods, the struc-
ture of relationships were built. We identified the models using the Pear-
son correlation matrix and the approach on the base of von Liebig law,
with K = 3 levels of components values. The structure of relationships
for both period is presented in Figs. 1 and 2. The notation on the graphs
corresponds to the models and is quiet understandable: the components
are presented as rectangulars connected by ovals presenting considered re-
lationships. For example, Λ(MIN, MID) = (+, −), that is clearly shown
on the graph.
Fig. 1. The structure of relationships for “high-performance” period. Rounded rectan-
gulars present the components of the system, the ovals include relationships between
the components.
Fig. 2. The structure of relationships for “low-performance” period.
- 68 -
Comparing the graphs in Fig. 1 and Fig. 2 shows a system-forming role
of the component MID for the “high-performance” period, in which MID
positively affected other three components. This affect disappeared in
the “low-performance’ period together with loss a stabilizing mechanism
through the relationship (+, −) between MID and MIN supporting a
dynamic equilibrium of the system.
These results are consistent with empirically established ideas about
significant positive role of fanfictions of medium size (MID) in a function-
ing of social networks of this category and their close relation to short-
sized fanfictions (MIN) representing a reaction of the most dynamic part
of users. Differences in role of OTHER correspond to significance of
“offtopic” as an index of deterioration in work of dedicated web-sites.
Our next example concerns the system relations of anthropometric
parameters of adolescents suffering diseases of cardiovascular system [13].
Anthropometry is important in school medical, in particular, for de-
termining the factors of predisposition of adolescents to cardiovascular
disorders. At the same time, among other drawbacks of currently used
anthropometric methods they often refer to insufficient use of systematic
approach, among other things, in description of regularities in formation
of body’s proportions in the individual development of adolescents.
Here we present a demo of application of DMDS for this purpose,
calculated on the material of adolescents anthropometry with arterial
hypertension and other forms of cardiovascular disorders. Body compo-
sitions related to overweight plays an important role in development of
arterial hypertension. Taking that into account, the models for four fol-
lowing components were built: hip circumference, waist circumference,
chest circumference, and shoulder breadth divided by height of a subject.
The Spearman correlation and Liebig’s approach with K = 3 levels of
components were used in modeling.
Comparison of these graphs has revealed a different role of such an-
thropometric parameters as the hip circumference for two group of ado-
lescents under investigation. In the group with disorders different from
arterial hypertension high values of hip circumference increase other three
components. Simultaneously, shoulder breadth negatively affects hip cir-
cumference, that should form a proportion of male’s future body perceiv-
ing by subconscious as harmonious on the base on evolutionary history
and recognized as such by modern physiology and medicine — the pro-
portions of male “triangle” directed beneath by edge. The structure of
relationships in the group with hypertension prevents the formation of
such a standard and associates with the accumulation of a depot fat in
- 69 -
Fig. 3. The structure of relationships for adolescents without arterial hypertension.
Fig. 4. The structure of relationships for adolescents with arterial hypertension.
certain parts of a human body: relatively high values of the hip circum-
ference negatively affects shoulders breadth and chest circumference, not
directly affecting waist circumference, on which shoulders breadth posi-
tively influences.
These results, regarded by authors as preliminary, do not contradict
known facts about the impact of anthropometric parameters on the risk
of development of hypertension in adolescents groups.
Our last example was taken from industrial fishery of Atlantic cod
(Gadus morhua) at North Sea. The fishery of the cod plays important
role in the economy of several countries and provokes considerable interest
to use of mathematical models in industrial ichthyology describing large
fluctuations of catching [14] (well-known example of this kind is collapse
of the Atlantic northwest cod fishery in 1992).
As the demo the additive stochastic model of relationships structure
between dimensional parameters of cod populations was considered. The
average fish body length (L), the difference between Upper Length Bound
- 70 -
and Lower Length Bound (vL), the average stomachs weight (M), and
the average weight of preys of cod (dM) were taken as components of the
model. Additive stochastic models were built according to data of Inter-
national Council for the Exploration of the Sea for two years (1984 and
1989) preceding to rapid changes of CPUE (the catch per unit effort). We
used the model with K = 4 levels of components values. In the matrix
Table 1. Relationships matrices for 1984 and 1989
1984 1989
L vL M dM L vL M dM
L -0.936 -0.379 0.893 0.581 L -0.843 0.137 0.953 0.059
vL 0.325 -0.737 -0.405 0.519 vL 0.963 -0.721 -0.997 0.494
M -0.184 -0.868 0.969 -0.081 M -0.882 -0.054 0.788 0.224
dM 0.016 -0.941 0.999 -0.028 dM 0.091 0.066 0.941 -0.995
corresponding to 1984, which precedes significant (till 1990) decrease of
catching, there are large (above 0.85) negative effects of high values of vL
on M and dM. That is, increasing the diversity of dimensional character-
istics of the cod population, that improves the consumption possibilities of
forage reserve by the cod, leads to exhaustion of food resources (reducing
the number of available preys) and deterioration of preys quality (reduc-
ing the average size of forage organisms), and results in deterioration of
food supply of the cod, that lowers the values of M and dM.
In the matrix corresponding to 1989, which precedes sharp increase of
CPUE, recorded a year later, in 1991, there exist extremely small (below
0.07) negative effects of high values of vL on M and dM. In this case,
the increasing diversity of sizes, that enhances abilities of consumption
of forage reserve, does not lead to exhaustion and deterioration of the
latter. This result of modeling explains differences described above in the
dynamics of catching in accordance with modern concepts of industrial
ichthyology. We also note the difference in the value of positive influence
of L on vL: 0.325 and 0.963 for 1984 and 1989 correspondingly.
Presented results bring hope for the possibility of developing meth-
ods for a forecast of cod catching with use of the stochastic models of
this class, built on the base of actual material on size structure of the
population.
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4 Conclusion
In the paper we followed the established framework in model develop-
ment, appropriated for natural sciences. Typical approach in develop-
ment, among others, comprises the data selection, specification of assump-
tions and simplifications, selection of a mathematical modeling frame-
work, estimation of parameter values, model diagnostics, model valida-
tion, model refinements and model application. It’s clear, that all these
stages of building mathematical models for biological systems are too
complicated, but the most difficult task among them is the model pa-
rameters estimation for identifying structure in the underlying biological
networks.
The models presented in the paper are created for description of bio-
logical and ecological systems, based on pairwise relationships character-
ized by the direction (positive, negative, or neutral) for both models and
by the strength varied from 0 to 1 in the stochastic model only.
The task of parameter estimation is a true challenging problem for
both models and requires development of special algorithms of numeri-
cal optimization. For example, if the system has N components and the
number of levels is to be assumed K, for the first deterministic model
the number of initial states is equal to K N and the number of possible
2
relationships’ structures is equal to 3N . For solving the stated optimiza-
tion problem (6), one should built the minor (2) with use of an initial
state and a relationships’ structure, calculate correlation matrix P and
calculate the distance (5). So, the exhaustive search of both initial states
2
and relationships’ structures jointly gives us K N 3N variants, that is a
huge number for even moderate N and K.
The case studies presented in the paper, considered by the authors
as preliminary and illustrating, offer the prospects of applications of pro-
posed models.
The results of modeling of system aspects in anthropometry of ado-
lescents present the approaches to use of this simple and cheap method
for identifying the risk groups of the progress of arterial hypertension.
These approaches may be applied in school medicine an, if necessary, in
extreme situations for mass screening as well.
The investigation of system factors of functioning of web-site dedi-
cated to fiction about characters from original works about Harry Potter,
due to use of components of the system, that are invariant to the content
of the web-site, may have a broader meaning in analysis of the social
networks performance.
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The model of the cod population as a whole does not contradict known
facts on the role of fish size and state of a forage reserve in the popula-
tion dynamics. At the same time, these results reveal some promises and
can be used in the development of approximate methods for prediction of
populations of commercial fish with use of relatively simple and inexpen-
sive methods of data acquisition, including even the commercial reports
concerning the assortment of fish products.
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