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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Complex systems and physics education</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Andrii O. Bielinskyi</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Arnold E. Kiv</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Yuliya O. Prikhozha</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Mykola A. Slusarenko</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Vladimir N. Soloviev</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Ben-Gurion University of the Negev</institution>
          ,
          <addr-line>P.O.B. 653, Beer Sheva, 8410501</addr-line>
          ,
          <country country="IL">Israel</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>Kryvyi Rih State Pedagogical University</institution>
          ,
          <addr-line>54 Gagarin Ave., Kryvyi Rih, 50086</addr-line>
          ,
          <country country="UA">Ukraine</country>
        </aff>
      </contrib-group>
      <fpage>56</fpage>
      <lpage>80</lpage>
      <abstract>
        <p>Synergetics as a scientific area of research is in demand by society. The context of synergetics makes it possible for scientists of diferent specializations to interact fruitfully in the language of systematic understanding and search for new solutions. The presented work raises the question of how the theory of self-organization can help in the reformation of the higher education system, why this is relevant, and what can lead to the training of both teachers and students within the framework of an interdisciplinary approach. In the future, we will highlight the most important characteristics of complex systems and the simplest and at the same time conceptually simplest methods for analyzing complexity. As part of the complex systems modeling course, which will first be presented to students of physics and mathematics, and then, possibly, to students of other specialties, we present signals of seismic activity, gravitational waves and magnetic activity, and demonstrate how we can identify critical or crash phenomena in such systems. This kind of analysis can serve as a good basis for the formation of professional skills and universal competencies.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;synergetics</kwd>
        <kwd>complex systems</kwd>
        <kwd>non-equilibrium</kwd>
        <kwd>self-organization</kwd>
        <kwd>interdisciplinarity</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        In 2021, Syukuro Manabe, Klaus Hasselmann, and Giorgio Parisi were awarded the Nobel Prize
in Physics “for groundbreaking contributions to our understanding of complex physical systems”
[
        <xref ref-type="bibr" rid="ref1">1</xref>
        ]. That is a sign that the study of complex systems is of paramount importance. Nevertheless,
we need to deal with the problems of their implementation in the educational process.
      </p>
      <p>The education system in the world today is in a state of crisis. This is evidenced by the
following trends: a further increase in the number of illiterate people in the world; the widespread
decline in the quality of education; the growing gap between education and culture, education
and science; alienation of the student from the educational process.</p>
      <p>
        This situation in the world at the present stage makes the problem of finding a new paradigm
of education urgent, since the possibility of sustainable development of society, successful
overcoming of global problems, regional and national conflicts characteristic of the present
time of the development of civilization is closely related to the achieved level of education of
all members of society [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ]. But the education system is always based on a certain scientific
understanding of the world and man, which determines the goals and objectives of education,
its content, principles and methods.
      </p>
      <p>The heyday of education in the XVII-XVIII centuries, which happened through the
development and spread of classical mechanics of the New Time, led to the determination of the picture
of the world, where the studied elements are unchangeable, and the laws of classical mechanics
are universal and apply to all types of motion of matter.</p>
      <p>In such a world there was no place for chance, and irreversibility and probability were usually
associated with the incompleteness of knowledge. In this case, each phenomenon has a cause
and at the same time there is a cause of other phenomena. Cause and efect form a chain that
comes from the past, permeates the present and disappears in the future. This meant that all
the processes taking place in the world were predetermined and led to the search for initial
elements, having discovered which, it is possible to accurately predict the future.</p>
      <p>Therefore, such ideological and methodological principles as rationalism, determinism,
mechanismism and reductionism began to dominate in scientific knowledge, which also had a decisive
influence on the education system: on the forms of knowledge acquisition, presentation of
material, organizational principles of education.</p>
      <p>
        The discovery by synergetics of the processes of self-organization in inanimate nature
clearly shows that the transition from disorder to order, accompanied by the emergence of
self-organization and stable structures, the replacement of old structures with new ones
occurs according to specific internal laws inherent in certain forms of the movement of matter.
Ultimately, it is the qualitative and quantitative criteria of self-organization that characterize
the level of complexity and perfection of the corresponding forms of movement [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ]. Based
on these ideas, it is possible to develop a classification of types, forms, properties of matter
according to their degree of complexity, perfection of organization, and thereby the degree
of development. In this regard, development itself appears as a very complex, self-organizing
process of movement from simple to complex, from less organized and perfect to more organized
and perfect. In other words, development, in contrast to the movement that characterizes any
changes in general, acts as a directed change associated with the emergence of a new one.
      </p>
      <p>The post-non-classical stage of the development of science shows that rigid determinism
and reductionism, which serve as the basis of the mechanistic view of the world, cannot be
considered as universal principles of scientific knowledge, since an extensive class of phenomena
and processes does not fit into the framework of linear, equilibrium and reversible schemes. In
the world around us, a very real irreversibility plays an essential role, which is the basis of the
majority of self-organization processes. Reversibility and rigid determinism in the world are
applicable only in simple limiting cases, and irreversibility and randomness should be considered
not as an exception, but as a general rule.</p>
      <p>To integrate the synergetics approach into the educational process, it is important to instill
in students ways of setting and solving problems of being and developing complex systems
in various spheres: economic, social, natural, etc. It is equally important, at the beginning of
studying the methods of studying complex systems, to instill in students at first or repeat with
them the concepts of self-organization, chaos, destructive phenomena, to voice the diference
between complex and complicated systems, etc.</p>
      <p>
        Complex systems are a field of research that is now acquiring the characteristic features of a
well-formed area of science with its own object, conceptual apparatus, and methods of analysis
[
        <xref ref-type="bibr" rid="ref4">4</xref>
        ]. The concept of a complex system is gradually becoming one of the fundamental concepts of
modern science, or, more broadly, it is increasingly appearing in a general cultural context. The
expansion of the scope of application of this concept, as well as the identification and awareness
of an increasing number of phenomena where it is applicable, causes dificulties in its exact
definition. Although the science of complex systems covers a broad interdisciplinary field of
research, the methods and concepts of physics (dynamical systems theory, quantum mechanics,
statistical physics) are central to it.
      </p>
      <p>So, the processes of self-organization in non-equilibrium conditions correspond to the
dialectical interaction between chance and necessity, fluctuations and deterministic laws. Near
bifurcations, the main role is played by chaos, randomness, while deterministic connections
dominate in the intervals between bifurcations. The ways of development of self-organizing
systems are not predetermined. Probability appears not as a product of our ignorance, but as an
inevitable expression of chaos at the points of bifurcations. This means the end of the classical
ideal of omniscience and creates the need to revise the principle of mechanical rationalism as
the dominant scientific explanation of reality. The traditional education system, based on the
principles of classical science, cannot efectively fulfill the role of a means of mastering the
world by a person.</p>
      <p>Hence, there is a need to integrate the principles and ideas of the complex systems paradigm
in the sphere of education.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Analysis of previous studies</title>
      <p>
        Analysis of scientific sources and publications shows that today there is an opinion that
synergetics could provide significant assistance in the search for a new paradigm of education.
A synergistic approach to understanding patterns operating in nature is associated with the
names of Haken [
        <xref ref-type="bibr" rid="ref5 ref6 ref7 ref8">5, 6, 7, 8</xref>
        ], Haken and Schiepek [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ], Nicolis and Prigogine [
        <xref ref-type="bibr" rid="ref10">10</xref>
        ], Prigogine and
Stengers [
        <xref ref-type="bibr" rid="ref11 ref12">11, 12</xref>
        ], Prigogine [
        <xref ref-type="bibr" rid="ref13 ref14">13, 14</xref>
        ]. Some scientists believe that synergetics, as a theory of
self-organization of complex systems, describes the general (common) that is in their
development, education is a complex system, and therefore synergetics, which today is developed by
various branches of scientific knowledge, necessarily becomes its new philosophy. However,
despite the existence of a suficient number of works devoted to the application of synergetics
in various spheres of human activity, the methodological and practical context of synergetics
in the philosophy of education remains insuficiently developed. This is especially true for
applying a synergistic approach to understanding the higher education system.
      </p>
      <p>
        When forming interdisciplinary specialists, a significant component may be the
humanitarization of education [
        <xref ref-type="bibr" rid="ref15">15</xref>
        ]. It is humanitarization that is designed to provide an educational
synthesis of humanitarian, technical and natural science disciplines based on multi-level
integration of the entire complex of knowledge. The growing trend of all scientific knowledge,
which manifests itself in the transition from focusing on individual disciplines studied in the
course of higher education, to strengthening interdisciplinary ties, requires qualitatively new
approaches to the content of education and reorientation in teaching. Humanitarization and
interdisciplinarity of education involve not only the intensive introduction of humanities
disciplines into purely technical higher educational institutions, but also the enrichment of Natural
Science and technical disciplines with material that reveals the struggle of scientific ideas, the
human destinies of scientists-discoverers, the dependence of socio-economic and scientific
progress on personal and moral qualities of a person, his creative abilities. In contrast to the
traditional interdisciplinary approach in education, the goal is not only to provide knowledge,
but also to teach to hear and understand colleagues working in diferent specialties, to develop
skills of dialogue between specialists in diferent branches of scientific knowledge. The need for
such a dialogue is becoming more and more palpable. Since the theoretical physicist Hermann
Haken introduced this concept into scientific use [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ], the world has been accumulating some
experience in the use of synergetics and in the study of social and educational systems.
      </p>
      <p>As Andrushchenko and Svyrydenko [16] notes, “... domestic scientific schools are not
always ready to accept the success of other schools and directions, when traditionalism and
conservatism enter the fight against innovation; threats of marginalization of carriers of foreign
experience in the educational or scientific environment are actualized”. These processes in their
content, scientists believe, contradict the logic of scientific cooperation, the spirit of partnership
and exchange of views, in which the long-term experience of the closed educational system, its
focus on ensuring the ideological function of education plays an important role. The nonlinear
complexity of methodological renewal, thanks to the creativity of creative processes, creates
new horizons for the emerging future [17]. This idea is supported by Kremen and Illyin [18],
noting that the principles and ideas of synergetics have significant heuristic and
methodological potential. In this regard, scientists believe that a synergistic approach to education and
upbringing can be the basic one for solving many problems in the field of education.</p>
      <p>When using and teaching approaches that are part of the synergetics paradigm, as already
noted, chaos seems to be the engine of change. From the point of view of synergetics, personality
development appears as a constant movement from one state of the system to another, in which
chaos, chance, creation/destruction, passage of bifurcation points, etc.are natural states of the
system, successively replacing each other, building a continuous chain of transformations [19].
Research conducted in schools and universities shows that interactive chaotic environments
are very productive for developing creative thinking. The results of work in this area were
presented by Davis-Seaver et al. [20], who analyzed the learning process at three levels – from
a single point of balance, statement of fact, statement of a single point of view to learning on
the verge of chaos, when there are many points of view, when reasoning develops in diferent
directions, when students listen to the opinions of others and on this basis develop their own
judgments. The role of the teacher is not to spread knowledge and evaluate the correctness of
judgments, but to monitor the progress of reasoning and transfer the learning process from
one level to another. As a result, the understanding becomes deeper, more versatile, and the
incentives for learning are largely created by the energy of the group, and not by the diligence
of the teacher. In the context of revealing a person’s creative abilities, a synergistic approach to
education seeks not to eradicate chaos, but to find the relationship between order and disorder
that would be most fruitful [21].</p>
      <p>
        The above-mentioned concept of chaos from the point of view of synergetics loses its negative
connotation. As Prigogine and Stengers [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ] notes, instability can be a condition for stable and
dynamic development. Only systems that are far from equilibrium are able to organize and
evolve spontaneously. Thus, there is no development without instability. And if the system is
strict against the implementation of new units, new units (‘innovators’) die”. In higher education,
self-organizing systems are the Student, Teacher, their interrelation, etc. [22].
      </p>
      <p>Jacobson and Wilensky [23], Wilensky and Jacobson [24] emphasize diferent research issues
that need to be explored. They present such principles in studying complex phenomena as
• experiencing complex systems phenomena;
• making the complex systems conceptual framework explicit [25];
• encouraging collaboration, discussion, and reflection; the design of environments for
learning about complex systems needs to take advantage of lessons learned from the
extensive research on pedagogy that foster collaboration, discussion, and reflection [ 26];
• constructing theories, models, and experiments;
• learning trajectories for deep understandings and explorations.</p>
      <p>With a given appropriate conceptual and representational scafolding in the learning
environment, students should be able to tap into their everyday experiences and channel and enhance
these experiences to construct understandings of complex systems that are cognitively robust.
Nowadays, students should have more possibilities to explore world through computational
modeling which progressive scientists use almost everyday.</p>
      <p>
        Jackson [27] and other, such as Pagels [28], have observed how the use of computational tools
in science allows dramatically enhanced capabilities to investigate complex and dynamical
systems that otherwise could not be systematically investigated by scientists. These computational
modeling approaches include cellular automata, network and agent-based modeling, neural
networks, genetic algorithms, Monte Carlo simulations, and so on that are generally used in
conjunction with scientific visualization techniques. Examples of complex systems that have
been investigated with advanced computational modeling techniques include climate change
[29], urban transportation models [
        <xref ref-type="bibr" rid="ref16 ref17">30, 31, 32</xref>
        ], and economics [
        <xref ref-type="bibr" rid="ref18 ref19 ref20 ref21">33, 34, 35, 36</xref>
        ]. New communities
of scientific practice have also emerged in which computational modeling techniques, in
particular agent-based models and genetic algorithms, are being used to create synthetic worlds such
as artificial life [
        <xref ref-type="bibr" rid="ref22 ref23">37, 38</xref>
        ] and societies [
        <xref ref-type="bibr" rid="ref24">39</xref>
        ] that allow tremendous flexibility to explore theoretical
and research questions in the physical, biological, and social sciences that would be dificult or
impossible in “real” or nonsynthetic settings.
      </p>
      <p>
        Methodology of nonlinear synthesis based on scientific principles evolution and co-evolution
of complex structures of the world, can form the basis of futurological research, designing
various ways of human development into the future [
        <xref ref-type="bibr" rid="ref25">40</xref>
        ]. As the environmental, economic,
and political problems of humanity have become global, complex and nonlinear, traditional
ideas about individual responsibility are becoming questionable. We need to study and teach
new models of collective behavior that take into account the diferent degrees of our individual
abilities and understanding of what is happening.
      </p>
      <p>We believe that the study of the apparatus of physics, graph theory, and computer science is
now of paramount importance for the further development of both our society and the entire
universe.</p>
      <p>
        In further we need to understand how to grow an interest of students in constructing and
revising computational models with multi-agent or qualitative modeling software, and how
model building activities may enhance student conduct of real world experiments related to the
phenomena under consideration [
        <xref ref-type="bibr" rid="ref26 ref27 ref28">41, 42, 43</xref>
        ].
      </p>
    </sec>
    <sec id="sec-3">
      <title>3. The most important properties of complex systems to be studied</title>
      <p>
        Based on the previously described characteristics and the direction in which we should move, it
becomes clear that synergetics (the theory of complex systems) is the foundation of almost any
system. Including pedagogical. Although the initial direction of research within this paradigm
was physical systems, the latest objects of research on various manifestations of complexity
also appear in the context of business organization and economics. For example, Wheatley [
        <xref ref-type="bibr" rid="ref29">44</xref>
        ]
suggests that we view organizations as being more like living organisms than machines. As
such, we need to modify traditional views on controlling organizations. Wheatley [
        <xref ref-type="bibr" rid="ref29">44</xref>
        ] argues
that organizations are dynamic, nonlinear networks of relationships and cannot be separated
into parts while maintaining their essential identity.
      </p>
      <p>In complex systems, it is worth highlighting that they are
• dynamic;
• non-equilibrium and have the potential to change suddenly and may take one path out of
an infinite number of others (bifurcate);
• open systems, that is interchange energy (and information) with their surroundings;
• depended. What happens next depends on what happened previously;
• systems where the whole is more than the sum of its parts;
• causal and yet indeterminate;
• irreversible, since the interaction of parts together is transforming;
• multi-agent. They composed of a diversity of agents that interact with each other, mutually
afect each other, and in so doing generate novel, emergent behavior for the system as a
whole. The system is constantly adapting to the conditions around it and over time it
evolves;
• co-evolving and move spontaneously towards the edge of chaos.</p>
      <sec id="sec-3-1">
        <title>3.1. Time series data</title>
        <p>
          In order to maintain students’ interest in studying complex systems and their corresponding data
analysis tools, programming languages, etc. [
          <xref ref-type="bibr" rid="ref30 ref31">45, 46</xref>
          ], it is important to select truly interesting
and complex systems (series). It is equally important that the studied systems are within
the framework of the specialty that students are guided by. However, since we strive for an
interdisciplinary approach, the study, for example, by biologists of the corresponding nonlinear
methods on the example of the same socio-economic series or physical ones can also be beneficial
for general development.
        </p>
        <p>
          Complexity theory is subdivided into hard and soft complexity. Hard complexity theory
stands for analytical analysis that concern with the nature of reality, while soft complexity aims
to describe social and living systems. Davis and Sumara [
          <xref ref-type="bibr" rid="ref32">47</xref>
          ] proposes such term as “complexity
thinking” which lies somewhere in between hard and soft skills. We support such idea and would
like to promote it among ordinary citizens who are not specialists and, particularly, among
universities and their student. Focusing on interdisciplinarity, both hard and soft skills, teachers
and students will be more creative and productive in their further research. Knowing about
interconnections across diferent disciplines, there are much more possibilities for collaborative
research between diferent faculties and there is larger probability that people will be able to
ifnd common topics for communication and will be engaged to cooperate.
        </p>
        <p>The goal of this work is to present the basic characteristics of complex systems, which should
be introduced to students during the course of studying complex systems, and the basic sets of
methods that allow analyzing the varying randomness (complexity) of the system during the
development of the studied signals.</p>
        <p>In this paper, we present some of the most fundamental, applied, robust, and powerful
methods on the example of three physical signals: seismic (SEI), gravitational wave (GW), and
the distribution storm time (Dst) index.</p>
        <p>
          SEI dataset constructed by Bladford [
          <xref ref-type="bibr" rid="ref33">48</xref>
          ]. Each event has 2048 points fixed at a seismic
recording station in Scandinavia.
        </p>
        <p>We used GW data GW150914 from Events of LIGO Open Science Center and select strain
data (H1 and L1) after noise subtraction [49] (https://www.ligo.org/detections/GW150914.php).</p>
        <p>The Dst index is an index of magnetic activity derived from a network of nearequatorial
geomagnetic observatories that measures the intensity of the globally symmetrical equatorial
electrojet (“ring current”). Dst is maintained at National Centers for Environmental Information
[50] from 1957 to the present. Dst equivalent equatorial magnetic disturbance indices are derived
from hourly scalings of low-latitude horizontal magnetic variation. They show the efect of the
globally symmetrical westward flowing high altitude equatorial ring current, which causes the
“main phase” depression worldwide in the H-component field during large magnetic storms.</p>
        <p>In this paper, the time series of hourly values of the storm on March 13, 1989 is investigated.
It is the strongest storm in the space age in several ways; the power system of the province of
Quebec was out of order. The peak of the storm falls in the middle of the time series (point
1000).</p>
        <p>In order to study changes of complexity dynamically, i.e., to get not only one value that
will characterize the whole system, but an array of values, where each value will reflect the
complexity of a signal in a specific period, we use sliding window approach [51].</p>
        <p>In figure 1 is presented the dynamics of all physical signals that could be studied during
physics classes. However, students of other faculties can also be interested.</p>
      </sec>
      <sec id="sec-3-2">
        <title>3.2. Fat-tailed distribution</title>
        <p>When studying complex systems, we inevitably encounter power distributions characterized by
thick tails. A classic example is the power-law of dividing words by their frequency of use in a
text, known as Zipf’s law [52].</p>
        <p>In economics, this is the law of wealth distribution among individuals [53]; in demography,
the distribution of cities by their size [54]; in biology, the distribution of the size of forest patches
[55]; in scientometry, the distribution of citations [56]. In general, a wide class of phenomena
is described in the framework of distributions with a degree dependence, but the researcher
(student) will have to find out the nature of such a dependence, which can be caused by many
factors: critical phenomena, processes with preference, self-organized criticality, multiplicative
processes with connections, optimization and path-dependent nonergodic processes, the phase
space of which decreases with evolution [57, 58, 59, 60, 61].</p>
        <p>First of all, it will be important to build an empirical distribution for our data (figure 2). Having
visualized the series we study in this paper, we can already be convinced of the non-Gaussian
dynamics of the presented systems.</p>
        <p>
          In the course of our research, we have determined that the Lévy  -stable distribution most
successfully covers the key statistical characteristics of both the economic [
          <xref ref-type="bibr" rid="ref34">62, 63, 64</xref>
          ] and those
systems presented in this paper. Figures 3a to 3c show the window dynamics of the  index
derived from the Lévy distribution that characterizes the “heaviness” of tails.
        </p>
      </sec>
      <sec id="sec-3-3">
        <title>3.3. Multifractality</title>
        <p>
          When studying various types of systems, we often encounter both fractal (self-similar) structures
and sets of diferent fractal dimensions [
          <xref ref-type="bibr" rid="ref35">65</xref>
          ]. In such problems, it is necessary to take into account
the entire range of critical indicators that characterize diferent moments in the distribution of
observed quantities. Such properties usually relate to the term “multifractality” [
          <xref ref-type="bibr" rid="ref36">66</xref>
          ].
        </p>
        <p>
          There are several diferent algorithms that allow the obtention of multifractal spectra from
time series. The most famous is the MF-DFA [
          <xref ref-type="bibr" rid="ref37 ref38 ref39">67, 68, 69</xref>
          ].
        </p>
        <p>
          Based on the MF-DFA procedure, we select the maximum value of such a quantitative
characteristic of multifractality as the singularity strength [
          <xref ref-type="bibr" rid="ref40">70</xref>
          ], although in the corresponding
section of fractal (multifractal) analysis, it would be necessary to characterize and demonstrate
the dynamics of all multifractality indicators. The following figure shows the window dynamics
of the maximum value of the singularity strength.
        </p>
      </sec>
      <sec id="sec-3-4">
        <title>3.4. Network analysis</title>
        <p>
          Equally important is the network analysis of complex systems. Today, networks play a central
role in modeling complex systems, as they ofer a way to describe diferent types of relationships
between agents that act as endpoints in the network. Complex networks can characterize
information, social, economic, biological, neural, and other systems [
          <xref ref-type="bibr" rid="ref41 ref42 ref43 ref44">71, 72, 73, 74</xref>
          ]. For example,
a society can be represented as a network, where each individual (university, wealth, city) can
be represented as nodes of a graph, and the connection between them through edges. For
cities, edges can represent a road, where the possibilities of movement can vary, and therefore a
diferent weight can be determined for each edge.
        </p>
        <p>In general, the computer network model is a random graph, the law of mutual arrangement
of edges and vertices for which is defined by the probability distribution.</p>
        <p>The simplest of networked objects, so-called Erdös-Rényi, or random graphs. Such graphs can
be characterized within the framework of the Poisson distribution, but most complex systems,
as already noted, are characterized within the framework of distributions with heavy tails.</p>
        <p>One of the most interesting characteristics of networks is the vertex degree. The vertex degree
distribution for many real-world networks shows a power-law dependence. Such networks are
called scale-independent. Scale-free networks are often characterized by very short average
distances between randomly chosen pairs of nodes that may have a strong impact on the whole
dynamics.</p>
        <p>
          In addition to the topology of graphs, you can also study their quantitative characteristics.
In our case, using the window procedure, we get a variable graph representation of our signal
over time. For the presented work, we calculated the maximum vertex degree of the graph
(), since this measure is one of the conceptually simplest measures, although many other
measures can be represented. It is worth noting that there are also various algorithms for
converting a time series to a graph. We would like to emphasize the visibility graph algorithms
[
          <xref ref-type="bibr" rid="ref34 ref45 ref46 ref47">64, 75, 76, 77, 78</xref>
          ] (figure 5) and one based on recurrence analysis [79] (figure 6).
        </p>
      </sec>
      <sec id="sec-3-5">
        <title>3.5. Recurrence analysis</title>
        <p>Processes in nature are characterized by pronounced recurrent behavior, such as periodicity or
irregular cyclicity.</p>
        <p>Moreover, the recurrence (repeatability) of states in the sense of passing a further trajectory
quite close to the previous one is a fundamental property of dissipative dynamical systems. This
property was noted in the 1880s by the French mathematician Henri Poincaré and subsequently
formulated in the form of the “recurrence theorem”, published in 1890 [80].</p>
        <p>The essence of this fundamental property is that, despite the fact that even the smallest
perturbation in a complex dynamical system can lead the system to an exponential deviation
from its state, after a while the system tends to return to a state that is somewhat close to the
previous one, and goes through similar stages of evolution.</p>
        <p>In 1987, Eckmann et al. [81] proposed a method for mapping the recurrence of phase space
trajectories to  ×  matrix. The appearance of a recurrence diagram allows us to judge
the nature of processes occurring in the system, the presence and influence of noise, states of
repetition and fading (laminarity), and the implementation of sudden changes (extreme events)
during the evolution of the system. If you look at recurrent diagrams in more detail, you can find
small-scale structures (textures) consisting of simple points, diagonal, horizontal, and vertical
lines, which in turn correspond to chaotic, repetitive, or laminar states.</p>
        <p>
          Using combinations of these states, Zbilut and Webber [82], Webber and Zbilut [83] developed
a tool for calculating a series of measures based on the distribution of recurrent points on a
recurrence matrix. Later, the toolkit for quantitative recurrent analysis was supplemented by
Marwan and Kurths [84]. The tools of quantitative recurrent analysis include the recurrence
rate, determined by the ratio of recurrent points to the total number of points on the recurrence
matrix under study. In addition to the recurrence measure, in the course of analyzing complex
systems, it would be possible to present such measures as determinism, divergence, entropy,
trend, and so on [
          <xref ref-type="bibr" rid="ref34">78, 64, 51, 85, 86, 87, 88</xref>
          ].
        </p>
        <p>In this paper, we will focus on the recurrence rate and present it for the already specified
series (figure 7).</p>
      </sec>
      <sec id="sec-3-6">
        <title>3.6. Entropy and non-extensive statistics</title>
        <p>The Boltzmann-Gibbs statistical entropy and the classical statistical mechanics associated with
it are extremely useful tools for studying a wide range of simple systems that are characterized
by a small range of space-time correlations (short memory), the additivity of noise, the presence
of intense chaos, the ergodicity of dynamic processes, the Euclidean geometry of phase space,
the locality of interaction between elements, the Gaussian probability distributions, etc.</p>
        <p>The Boltzmann-Gibbs statistical entropy is a fundamental concept of the school section and
the university course of thermodynamics and statistical physics.</p>
        <p>
          In statistical mechanics, entropy denotes the number of possible configurations of a
thermodynamic system. The notion of entropy can be associated with the uncertainty in the system
[89, 90]. In 1948, Shannon [91] transformed classical statistical entropy to information entropy.
Since then, a number of other types of information entropy have been developed [
          <xref ref-type="bibr" rid="ref48 ref49 ref50">92, 93, 94, 95</xref>
          ].
        </p>
        <p>In order to study many real-world systems, it is necessary to go beyond the standard course
of thermodynamics, statistical physics, and classical Shannon entropy. A whole range of natural,
artificial and social systems, which, unlike those mentioned above, are characterized by a long
range of spatio-temporal correlations and non-Gaussian processes.</p>
        <p>Since the non-Gaussian and multifractal behavior of the studied systems was presented
previously, we will depict the autocorrelation function in the figure 8a, as it should demonstrate
an indicator decline. This fact will indicate the dependence of the following values on the
previous ones.</p>
        <p>It is also worth mentioning that such systems are characterized by multiplicative noise, the
presence of weak chaos (vanishing maximum Lyapunov exponent), non-ergodicity of dynamic
processes, hierarchy (usually multifractality) of the geometry of the phase space, the presence
of asymptotically power-law statistical distributions. A fairly wide class of these complex
systems (although not all) it is adequately described by non-additive statistics based on the
Tsallis parametric entropy.</p>
        <p>Figures 8b to 8d show the -Gaussian distribution from the Tsallis statistics for the considered
series in comparison with the classical Gaussian one.</p>
      </sec>
      <sec id="sec-3-7">
        <title>3.7. Reversibility and irreversibility</title>
        <p>The last characteristic that we would like to mention is time-reversibility. Temporary
irreversibility is a key property of non-equilibrium systems.</p>
        <p>
          Again, such systems are characterized by the presence of memory, while reversibility increases
with more noisy and unpredictable signals. Thus, by calculating the irreversibility, we determine
the degree of nonlinearity and predictability. It is important to note that the significant time
reversibility excludes linear Gaussian processes as a model of generating dynamics. Within the
framework of the systems we are considering, we need to think about methods of nonlinear
dynamics and non-Gaussian ones [
          <xref ref-type="bibr" rid="ref51 ref52">96, 97</xref>
          ].
        </p>
        <p>
          Over the past decade, various methods have been proposed for calculating the degree of
irreversibility in systems [
          <xref ref-type="bibr" rid="ref53 ref54 ref55 ref56 ref57 ref58 ref59 ref60">98, 99, 100, 101, 102, 103, 104, 105</xref>
          ] and we have presented how to use
some of them for crises identification [
          <xref ref-type="bibr" rid="ref47">77</xref>
          ]. For pedagogical purposes, along with the mentioned
concept of multifractality and entropy, we would like to present irreversibility based on the
multifractal approach [
          <xref ref-type="bibr" rid="ref60">105</xref>
          ] and permutation patterns [
          <xref ref-type="bibr" rid="ref59">104</xref>
          ]. The last mentioned approach could
be taught within the section of entropy approaches if we were teaching students. However, the
calculation of irreversibility based on graph theory is also possible [
          <xref ref-type="bibr" rid="ref55 ref56 ref57">100, 101, 102</xref>
          ].
        </p>
        <p>Figures 9a to 9c show the mentioned measures of irreversibility for the studied signals.</p>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>4. Conclusions</title>
      <p>The analysis of the adaptive nature of many complex systems led to the creation of methods
and the development of concepts that were successfully applied to describe formally similar
phenomena in chemical, biological, social and other systems of agents of non-physical nature.
It is sometimes argued that if physics is the science of the four fundamental forces that matter
interacts with.</p>
      <p>Remembering figures in the field of social sciences, it is still relevant to adapt theoretical
material and practical tasks of various fields of physics and higher mathematics to those
disciplines that students already study in the framework of social sciences.</p>
      <p>
        In this paper, we have presented some of the most significant approaches on the example of
SEI, GW, and Dst, but even more can be shown and much can be taught [
        <xref ref-type="bibr" rid="ref61 ref62">106, 107</xref>
        ]. The most
important thing is not just to convey information, but to interest the student in the right way.
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