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Phase Transitions and Emergent Phenomena: How Change Emerges through Basic Probability Models

A special issue of Entropy (ISSN 1099-4300). This special issue belongs to the section "Statistical Physics".

Deadline for manuscript submissions: closed (30 November 2020) | Viewed by 20733

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Statistical Physics Group, Centre for Fluid and Complex Systems, Coventry University, Coventry CV1 5FB, UK
Interests: phase transitions and critical phenomena; high-dimensional systems; finite-size scaling; boundary conditions; complexity science; interdisciplinary applications of statistical physics; scientometrics; sociophysics; digital humanities

Special Issue Information

Dear Colleagues,

Ludwig Boltzmann and contemporaries pioneered the development of statistical physics towards the end of the 19th century. The pillars on which the discipline rests include “bottom-up” theories of phase transitions and critical phenomena, built on other pioneering ideas and work such as that of Wilhelm Lenz and Ernst Ising at the start of the 20th century. In the words of Stephen Hawking, we are now in the “century of complexity”, moving on from basic laws that govern matter to how everything is connected to everything else.

Although Ising’s original investigations did not deliver the desired result of a phase transition, the idea that randomness coupled with gross simplification at the micro-level could explain changes of state at the macro-level was ground-breaking. Now we know the importance of dimensionality; interaction range; symmetries; whether the model is classical or quantum, equilibrium, or non-equilibrium, etc., in understanding the physics of change.

A vast body of research covers how all sorts of variants on such systems describe increasingly complex systems, but the essential idea to apply probabilistic considerations to simplified many-body systems was borrowed from socio systems. In recent times, with the emergence of the notion of “emergence”, the statistical physics of complex systems has re-embraced its interdisciplinary birthplace, delivering rich physics in and beyond physics and contributing to our understanding of the world.

This Special Issue focuses on models that are simplified at the micro level but complex at the macro level. We are interested in negative results like Ising’s as well as positive results, and, reflecting the birthplace of statistical physics, we welcome interdisciplinary considerations as well as traditional physics. Thus, this Issue focuses on the concept of change—how the simple can deliver the complex through non-trivial mechanisms, wherever they arise.

This special issue is dedicated to the fond memory of Professor Ian Campbell who has contributed so much to our understanding of phase transitions and emergent phenomena. In particular, Ian’s discovery of extended scaling, and his research into hyperscaling and spin glasses have contributed very significantly to theories of critical phenomena and we anticipate they will contribute more in the years to come. We are honored that Ian’s last paper (co-authored with Per-Håkan Lundow) is published in this special issue.

 

Prof. Dr. Ralph Kenna
Guest Editor

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Keywords

  • Phase transitions
  • Critical phenomena
  • Universality
  • Scaling
  • Statistical physics concepts applied to other disciplines

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Published Papers (6 papers)

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Research

22 pages, 409 KiB  
Article
Exact Recovery of Stochastic Block Model by Ising Model
by Feng Zhao, Min Ye and Shao-Lun Huang
Entropy 2021, 23(1), 65; https://doi.org/10.3390/e23010065 - 2 Jan 2021
Cited by 2 | Viewed by 2818
Abstract
In this paper, we study the phase transition property of an Ising model defined on a special random graph—the stochastic block model (SBM). Based on the Ising model, we propose a stochastic estimator to achieve the exact recovery for the SBM. The stochastic [...] Read more.
In this paper, we study the phase transition property of an Ising model defined on a special random graph—the stochastic block model (SBM). Based on the Ising model, we propose a stochastic estimator to achieve the exact recovery for the SBM. The stochastic algorithm can be transformed into an optimization problem, which includes the special case of maximum likelihood and maximum modularity. Additionally, we give an unbiased convergent estimator for the model parameters of the SBM, which can be computed in constant time. Finally, we use metropolis sampling to realize the stochastic estimator and verify the phase transition phenomenon thfough experiments. Full article
Show Figures

Figure 1

Figure 1
<p>Illustration of Theorem 2.</p>
Full article ">Figure 2
<p>Experimental results.</p>
Full article ">
16 pages, 1003 KiB  
Article
(Four) Dual Plaquette 3D Ising Models
by Desmond A. Johnston and Ranasinghe P. K. C. M. Ranasinghe
Entropy 2020, 22(6), 633; https://doi.org/10.3390/e22060633 - 8 Jun 2020
Cited by 3 | Viewed by 3590
Abstract
A characteristic feature of the 3 d plaquette Ising model is its planar subsystem symmetry. The quantum version of this model has been shown to be related via a duality to the X-Cube model, which has been paradigmatic in the new and rapidly [...] Read more.
A characteristic feature of the 3 d plaquette Ising model is its planar subsystem symmetry. The quantum version of this model has been shown to be related via a duality to the X-Cube model, which has been paradigmatic in the new and rapidly developing field of fractons. The relation between the 3 d plaquette Ising and the X-Cube model is similar to that between the 2 d quantum transverse spin Ising model and the Toric Code. Gauging the global symmetry in the case of the 2 d Ising model and considering the gauge invariant sector of the high temperature phase leads to the Toric Code, whereas gauging the subsystem symmetry of the 3 d quantum transverse spin plaquette Ising model leads to the X-Cube model. A non-standard dual formulation of the 3 d plaquette Ising model which utilises three flavours of spins has recently been discussed in the context of dualising the fracton-free sector of the X-Cube model. In this paper we investigate the classical spin version of this non-standard dual Hamiltonian and discuss its properties in relation to the more familiar Ashkin–Teller-like dual and further related dual formulations involving both link and vertex spins and non-Ising spins. Full article
Show Figures

Figure 1

Figure 1
<p>Flipping the value of the Ising spins on a face of a single cube in the <math display="inline"><semantics> <mrow> <mn>3</mn> <mi>d</mi> </mrow> </semantics></math> plaquette Ising Hamiltonian <math display="inline"><semantics> <msub> <mi>H</mi> <mrow> <mi>κ</mi> <mo>=</mo> <mn>0</mn> </mrow> </msub> </semantics></math> does not change its contribution to the energy. The first cube configuration is the ferromagnetic state with all spins +. The spins at the corners of the dark shaded faces on the other three are −, the others +. All four of the single cube configurations shown have the same energy.</p>
Full article ">Figure 2
<p>The terms contributing to the X-Cube Hamiltonian. The cube <span class="html-italic">A</span> term is a product of the twelve <math display="inline"><semantics> <msup> <mi>τ</mi> <mi>x</mi> </msup> </semantics></math> spins on the edges of the cube and the three <span class="html-italic">B</span> “X” terms composed of <math display="inline"><semantics> <msup> <mi>τ</mi> <mi>z</mi> </msup> </semantics></math> spins lie in each of the three lattice planes as shown on the corner.</p>
Full article ">Figure 3
<p>One of the matchbox surfaces which satisfy the algebra of Equation (<a href="#FD18-entropy-22-00633" class="html-disp-formula">18</a>).</p>
Full article ">Figure 4
<p>The standard decoration transformation. Summing over the central spin <span class="html-italic">s</span> denoted by an open dot gives a new effective coupling <math display="inline"><semantics> <mrow> <mi>β</mi> <mo>=</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <mo form="prefix">log</mo> <mrow> <mo stretchy="false">[</mo> <mo form="prefix">cosh</mo> <mrow> <mo stretchy="false">(</mo> <mn>2</mn> <mover accent="true"> <mi>β</mi> <mo>˜</mo> </mover> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">]</mo> </mrow> </mrow> </semantics></math> between the spins on the end of the link.</p>
Full article ">Figure 5
<p>Four Possible ground state spin configurations on a cube for <math display="inline"><semantics> <msub> <mi>H</mi> <mrow> <mi>d</mi> <mi>u</mi> <mi>a</mi> <mi>l</mi> <mn>2</mn> </mrow> </msub> </semantics></math>. The initial cube again has all + spins and the <math display="inline"><semantics> <mrow> <mi>σ</mi> <mo>,</mo> <mi>τ</mi> <mo>,</mo> <mi>μ</mi> </mrow> </semantics></math> values are shown for the spins at the corners of the darker shaded flipped faces, with the other spins being positive. The directions of the anisotropic couplings in the Hamiltonian are indicated.</p>
Full article ">Figure 6
<p>Four possible ground state spin configurations on a cube for the Ashkin–Teller formulation of the dual Hamiltonian, <math display="inline"><semantics> <msub> <mi>H</mi> <mrow> <mi>d</mi> <mi>u</mi> <mi>a</mi> <mi>l</mi> <mn>1</mn> </mrow> </msub> </semantics></math>. The <math display="inline"><semantics> <mrow> <mi>σ</mi> <mo>,</mo> <mi>τ</mi> </mrow> </semantics></math> values are shown for the darker shaded flipped planes. The directions of the anisotropic couplings in the Hamiltonian are again indicated.</p>
Full article ">Figure 7
<p>The energy for <math display="inline"><semantics> <msub> <mi>H</mi> <mrow> <mi>d</mi> <mi>u</mi> <mi>a</mi> <mi>l</mi> <mn>2</mn> </mrow> </msub> </semantics></math> on lattices ranging from <math display="inline"><semantics> <msup> <mn>10</mn> <mn>3</mn> </msup> </semantics></math> to <math display="inline"><semantics> <msup> <mn>20</mn> <mn>3</mn> </msup> </semantics></math> from left to right. The lines joining the data points are drawn to guide the eye. Data from <math display="inline"><semantics> <msub> <mi>H</mi> <mrow> <mi>d</mi> <mi>u</mi> <mi>a</mi> <mi>l</mi> <mn>1</mn> </mrow> </msub> </semantics></math> is essentially identical.</p>
Full article ">Figure 8
<p>The energy for <math display="inline"><semantics> <msub> <mi>H</mi> <mrow> <mi>d</mi> <mi>u</mi> <mi>a</mi> <mi>l</mi> <mn>3</mn> </mrow> </msub> </semantics></math> on lattices ranging from <math display="inline"><semantics> <msup> <mn>10</mn> <mn>3</mn> </msup> </semantics></math> to <math display="inline"><semantics> <msup> <mn>18</mn> <mn>3</mn> </msup> </semantics></math> from left to right. The lines joining the data points are drawn to guide the eye.</p>
Full article ">Figure 9
<p>The energy histogram <math display="inline"><semantics> <mrow> <mi>P</mi> <mo stretchy="false">(</mo> <mi>E</mi> <mo stretchy="false">)</mo> </mrow> </semantics></math> for <math display="inline"><semantics> <msub> <mi>H</mi> <mrow> <mi>d</mi> <mi>u</mi> <mi>a</mi> <mi>l</mi> <mn>3</mn> </mrow> </msub> </semantics></math> close to the estimated transition point at <math display="inline"><semantics> <mrow> <mi>β</mi> <mo>≃</mo> <mn>0</mn> <mo>.</mo> <mn>97</mn> </mrow> </semantics></math> on a <math display="inline"><semantics> <msup> <mn>10</mn> <mn>3</mn> </msup> </semantics></math> lattice.</p>
Full article ">Figure 10
<p>The time series of energy measurements obtained from cooling <math display="inline"><semantics> <mrow> <msup> <mn>20</mn> <mn>3</mn> </msup> <mo>,</mo> <msup> <mn>60</mn> <mn>3</mn> </msup> </mrow> </semantics></math> and <math display="inline"><semantics> <msup> <mn>80</mn> <mn>3</mn> </msup> </semantics></math> lattices from a hot start at <math display="inline"><semantics> <mrow> <mi>T</mi> <mo>=</mo> <mn>3</mn> <mo>.</mo> <mn>0</mn> </mrow> </semantics></math> at a rate of <math display="inline"><semantics> <mrow> <mi>δ</mi> <mi>T</mi> <mo>=</mo> <mn>0</mn> <mo>.</mo> <mn>00001</mn> </mrow> </semantics></math> per sweep. The traces are effectively indistinguishable.</p>
Full article ">Figure 11
<p>The time series of energy measurements obtained from cooling <math display="inline"><semantics> <mrow> <msup> <mn>20</mn> <mn>3</mn> </msup> <mo>,</mo> <msup> <mn>60</mn> <mn>3</mn> </msup> </mrow> </semantics></math> and <math display="inline"><semantics> <msup> <mn>80</mn> <mn>3</mn> </msup> </semantics></math> lattices from a hot start at a rate of <math display="inline"><semantics> <mrow> <mi>δ</mi> <mi>T</mi> <mo>=</mo> <mn>0</mn> <mo>.</mo> <mn>001</mn> </mrow> </semantics></math> per sweep.</p>
Full article ">
16 pages, 1670 KiB  
Article
Spin Glasses in a Field Show a Phase Transition Varying the Distance among Real Replicas (And How to Exploit It to Find the Critical Line in a Field)
by Maddalena Dilucca, Luca Leuzzi, Giorgio Parisi, Federico Ricci-Tersenghi and Juan J. Ruiz-Lorenzo
Entropy 2020, 22(2), 250; https://doi.org/10.3390/e22020250 - 22 Feb 2020
Cited by 4 | Viewed by 5204
Abstract
We discuss a phase transition in spin glass models that have been rarely considered in the past, namely, the phase transition that may take place when two real replicas are forced to be at a larger distance (i.e., at a smaller overlap) than [...] Read more.
We discuss a phase transition in spin glass models that have been rarely considered in the past, namely, the phase transition that may take place when two real replicas are forced to be at a larger distance (i.e., at a smaller overlap) than the typical one. In the first part of the work, by solving analytically the Sherrington-Kirkpatrick model in a field close to its critical point, we show that, even in a paramagnetic phase, the forcing of two real replicas to an overlap small enough leads the model to a phase transition where the symmetry between replicas is spontaneously broken. More importantly, this phase transition is related to the de Almeida-Thouless (dAT) critical line. In the second part of the work, we exploit the phase transition in the overlap between two real replicas to identify the critical line in a field in finite dimensional spin glasses. This is a notoriously difficult computational problem, because of considerable finite size corrections. We introduce a new method of analysis of Monte Carlo data for disordered systems, where the overlap between two real replicas is used as a conditioning variate. We apply this analysis to equilibrium measurements collected in the paramagnetic phase in a field, h > 0 and T c ( h ) < T < T c ( h = 0 ) , of the d = 1 spin glass model with long range interactions decaying fast enough to be outside the regime of validity of the mean field theory. We thus provide very reliable estimates for the thermodynamic critical temperature in a field. Full article
Show Figures

Figure 1

Figure 1
<p>Parameters of the RS solutions versus <math display="inline"><semantics> <msub> <mi>p</mi> <mi>d</mi> </msub> </semantics></math> in the case of <math display="inline"><semantics> <mrow> <mi>τ</mi> <mo>=</mo> <mi>h</mi> <mo>=</mo> <mn>0.1</mn> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>y</mi> <mo>=</mo> <mn>2</mn> <mo>/</mo> <mn>3</mn> </mrow> </semantics></math>. The merging of the three curves takes place at <math display="inline"><semantics> <mrow> <msub> <mi>p</mi> <mi>d</mi> </msub> <mo>=</mo> <msubsup> <mi>p</mi> <mi>d</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>τ</mi> <mo>,</mo> <mi>h</mi> <mo>,</mo> <mi>y</mi> <mo>)</mo> </mrow> <mo>=</mo> <mn>0.117033</mn> </mrow> </semantics></math>, while the crossing between the two curves takes place at <math display="inline"><semantics> <mrow> <msub> <mi>q</mi> <mi>EA</mi> </msub> <mrow> <mo>(</mo> <mi>τ</mi> <mo>,</mo> <mi>h</mi> <mo>,</mo> <mi>y</mi> <mo>)</mo> </mrow> <mo>=</mo> <mn>0.141942</mn> </mrow> </semantics></math>.</p>
Full article ">Figure 2
<p>Values of <math display="inline"><semantics> <mrow> <msub> <mi>q</mi> <mi>EA</mi> </msub> <mrow> <mo>(</mo> <mi>τ</mi> <mo>,</mo> <mi>h</mi> <mo>,</mo> <mi>y</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msubsup> <mi>p</mi> <mi>d</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>τ</mi> <mo>,</mo> <mi>h</mi> <mo>,</mo> <mi>y</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> plotted in the <math display="inline"><semantics> <mrow> <mo>(</mo> <mi>h</mi> <mo>,</mo> <mi>T</mi> <mo>=</mo> <mn>1</mn> <mo>-</mo> <mi>τ</mi> <mo>)</mo> </mrow> </semantics></math> plane for <math display="inline"><semantics> <mrow> <mi>y</mi> <mo>=</mo> <mn>2</mn> <mo>/</mo> <mn>3</mn> </mrow> </semantics></math>. The red bold curve is the dAT line, separating the paramagnetic and the spin glass phases. <math display="inline"><semantics> <msub> <mi>q</mi> <mi>EA</mi> </msub> </semantics></math> and <math display="inline"><semantics> <msubsup> <mi>p</mi> <mi>d</mi> <mo>*</mo> </msubsup> </semantics></math> merge on the dAT line, while their values in the spin glass phase have no physical meaning. Below the blue surface in the paramagnetic phase, the <math display="inline"><semantics> <mrow> <mi>p</mi> <mo>(</mo> <mi>x</mi> <mo>)</mo> <mo>=</mo> <mi>q</mi> <mo>(</mo> <mi>x</mi> <mo>)</mo> </mrow> </semantics></math> symmetry is broken.</p>
Full article ">Figure 3
<p>Free energies of the <math display="inline"><semantics> <mrow> <mi>p</mi> <mo>=</mo> <mi>q</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>p</mi> <mo>≠</mo> <mi>q</mi> </mrow> </semantics></math> RS solutions for <math display="inline"><semantics> <mrow> <mi>τ</mi> <mo>=</mo> <mi>h</mi> <mo>=</mo> <mn>0.1</mn> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>y</mi> <mo>=</mo> <mn>2</mn> <mo>/</mo> <mn>3</mn> </mrow> </semantics></math>. Below <math display="inline"><semantics> <mrow> <msubsup> <mi>p</mi> <mi>d</mi> <mo>*</mo> </msubsup> <mo>=</mo> <mn>0.117033</mn> </mrow> </semantics></math>, the free energy of the <math display="inline"><semantics> <mrow> <mi>p</mi> <mo>≠</mo> <mi>q</mi> </mrow> </semantics></math> solution is higher, and such a solution dominates over the symmetric one (<b>left panel</b>). The free energy difference goes as <math display="inline"><semantics> <msup> <mrow> <mo>(</mo> <msubsup> <mi>p</mi> <mi>d</mi> <mo>*</mo> </msubsup> <mo>-</mo> <msub> <mi>p</mi> <mi>d</mi> </msub> <mo>)</mo> </mrow> <mn>3</mn> </msup> </semantics></math>, as can be seen in the (<b>right panel</b>), where the black dot marks the value of <math display="inline"><semantics> <msubsup> <mi>p</mi> <mi>d</mi> <mo>*</mo> </msubsup> </semantics></math>.</p>
Full article ">Figure 4
<p>Difference between the one-step RSB (1RSB) free energies and <math display="inline"><semantics> <msub> <mi>F</mi> <mi>RS</mi> </msub> </semantics></math> for the two solutions with <math display="inline"><semantics> <mrow> <mi>τ</mi> <mo>=</mo> <mi>h</mi> <mo>=</mo> <mn>0.1</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>y</mi> <mo>=</mo> <mn>2</mn> <mo>/</mo> <mn>3</mn> </mrow> </semantics></math>, and <math display="inline"><semantics> <mrow> <msub> <mi>p</mi> <mi>d</mi> </msub> <mo>=</mo> <mn>0.05</mn> </mrow> </semantics></math>. We notice that the difference is very small, but clearly non-zero. Moreover, the maximum is achieved for a rather small value of m, thus limiting the difference with respect to the RS solution to very small values of <span class="html-italic">x</span> (we remind the reader that, in both 1RSB solutions, <math display="inline"><semantics> <mrow> <msub> <mi>p</mi> <mn>1</mn> </msub> <mo>≃</mo> <mi>p</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>q</mi> <mn>1</mn> </msub> <mo>≃</mo> <mi>q</mi> </mrow> </semantics></math>).</p>
Full article ">Figure 5
<p>Difference between the dominating 1RSB free energy and <math display="inline"><semantics> <msub> <mi>F</mi> <mi>RS</mi> </msub> </semantics></math> as a function of <span class="html-italic">m</span> (<b>left</b>) and <math display="inline"><semantics> <msub> <mi>p</mi> <mi>d</mi> </msub> </semantics></math> (<b>right</b>). The left panel shows that the location of the maximum of <math display="inline"><semantics> <msub> <mi>F</mi> <mi>RSB</mi> </msub> </semantics></math> slightly decreases when <math display="inline"><semantics> <msub> <mi>p</mi> <mi>d</mi> </msub> </semantics></math> grows, but the main effect is that, for any <span class="html-italic">m</span> value, <math display="inline"><semantics> <msub> <mi>F</mi> <mi>RSB</mi> </msub> </semantics></math> tends to move toward <math display="inline"><semantics> <msub> <mi>F</mi> <mi>RS</mi> </msub> </semantics></math> when <math display="inline"><semantics> <msub> <mi>p</mi> <mi>d</mi> </msub> </semantics></math> grows. The right panel shows that, for different <span class="html-italic">m</span> values, the free energy difference becomes zero very close to <math display="inline"><semantics> <msubsup> <mi>p</mi> <mi>d</mi> <mo>*</mo> </msubsup> </semantics></math>, marked with a black dot. Note that data in the region close to <math display="inline"><semantics> <msubsup> <mi>p</mi> <mi>d</mi> <mo>*</mo> </msubsup> </semantics></math> may have some uncertainty due to the extremely small free energy differences, which are of the order <math display="inline"><semantics> <mrow> <mi>O</mi> <mo>(</mo> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>12</mn> </mrow> </msup> <mo>)</mo> </mrow> </semantics></math>.</p>
Full article ">Figure 6
<p><math display="inline"><semantics> <mrow> <mi>χ</mi> <mrow> <mo>(</mo> <mi>q</mi> <mo>)</mo> </mrow> <mo>/</mo> <msup> <mi>L</mi> <mrow> <mn>2</mn> <mo>-</mo> <mi>η</mi> </mrow> </msup> </mrow> </semantics></math> versus <span class="html-italic">q</span> for <math display="inline"><semantics> <mrow> <mi>ρ</mi> <mo>=</mo> <mn>1.4</mn> </mrow> </semantics></math> (non-mean field region) and six different lattice sizes. Data in the upper panels have been measured with <math display="inline"><semantics> <mrow> <mi>T</mi> <mo>=</mo> <mn>1.7</mn> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>h</mi> <mo>=</mo> <mn>0.2</mn> </mrow> </semantics></math> and belong to the paramagnetic phase [<a href="#B16-entropy-22-00250" class="html-bibr">16</a>], thus showing that a transition to a spin glass phase can be induced merely by decreasing the overlap between the replicas. In the bottom panels, near or inside the thermodynamic spin glass phase, <math display="inline"><semantics> <mrow> <mi>T</mi> <mo>=</mo> <mn>1.2</mn> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>h</mi> <mo>=</mo> <mn>0.2</mn> </mrow> </semantics></math>. The crossing point of the curves for different lattice sizes is always very neat, as can be appreciated from the panels on the right that zoom in on the crossing region.</p>
Full article ">Figure 7
<p>The cumulative probability distribution <math display="inline"><semantics> <mrow> <mi>x</mi> <mo>(</mo> <mi>q</mi> <mo>)</mo> </mrow> </semantics></math> versus <span class="html-italic">q</span> for <math display="inline"><semantics> <mrow> <mi>ρ</mi> <mo>=</mo> <mn>1.4</mn> </mrow> </semantics></math> (non-mean field region), <math display="inline"><semantics> <mrow> <mi>h</mi> <mo>=</mo> <mn>0.2</mn> </mrow> </semantics></math>, and two values of the temperature: <math display="inline"><semantics> <mrow> <mi>T</mi> <mo>=</mo> <mn>1.7</mn> </mrow> </semantics></math> (<b>left panel</b>) and <math display="inline"><semantics> <mrow> <mi>T</mi> <mo>=</mo> <mn>1.2</mn> </mrow> </semantics></math> (<b>right panel</b>). The estimate for <math display="inline"><semantics> <msub> <mi>q</mi> <mi>EA</mi> </msub> </semantics></math> comes from the crossing of these curves.</p>
Full article ">Figure 8
<p>Behavior of <math display="inline"><semantics> <mrow> <msub> <mi>q</mi> <mi>c</mi> </msub> <mrow> <mo>(</mo> <mi>T</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>q</mi> <mi>EA</mi> </msub> <mrow> <mo>(</mo> <mi>T</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> for <math display="inline"><semantics> <mrow> <mi>ρ</mi> <mo>=</mo> <mn>1.4</mn> </mrow> </semantics></math> (<b>top-left panel</b> with <math display="inline"><semantics> <mrow> <mi>h</mi> <mo>=</mo> <mn>0.3</mn> </mrow> </semantics></math>, <b>middle-left panel</b> with <math display="inline"><semantics> <mrow> <mi>h</mi> <mo>=</mo> <mn>0.2</mn> </mrow> </semantics></math> and <b>bottom-left</b> with <math display="inline"><semantics> <mrow> <mi>h</mi> <mo>=</mo> <mn>0.1</mn> </mrow> </semantics></math>) in the non.mean field regime and <math display="inline"><semantics> <mrow> <mi>ρ</mi> <mo>=</mo> <mn>1.2</mn> </mrow> </semantics></math> (<b>top-right panel</b> with <math display="inline"><semantics> <mrow> <mi>h</mi> <mo>=</mo> <mn>0.3</mn> </mrow> </semantics></math> and <b>bottom-right panel</b> with <math display="inline"><semantics> <mrow> <mi>h</mi> <mo>=</mo> <mn>0.2</mn> </mrow> </semantics></math>) in the mean field regime. The crossing (or merging) of the curves identifies the thermodynamic phase transition to the spin glass phase (dAT line) because <math display="inline"><semantics> <mrow> <msub> <mi>q</mi> <mi>c</mi> </msub> <mo>&lt;</mo> <msub> <mi>q</mi> <mi>EA</mi> </msub> </mrow> </semantics></math> holds in the paramagnetic phase. Data shown are for the largest sizes (<math display="inline"><semantics> <mrow> <mi>L</mi> <mo>=</mo> <msup> <mn>2</mn> <mn>12</mn> </msup> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>L</mi> <mo>=</mo> <msup> <mn>2</mn> <mn>13</mn> </msup> </mrow> </semantics></math>).</p>
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10 pages, 497 KiB  
Article
Hyperscaling Violation in Ising Spin Glasses
by Ian A. Campbell and Per H. Lundow
Entropy 2019, 21(10), 978; https://doi.org/10.3390/e21100978 - 8 Oct 2019
Cited by 3 | Viewed by 2913
Abstract
In addition to the standard scaling rules relating critical exponents at second order transitions, hyperscaling rules involve the dimension of the model. It is well known that in canonical Ising models hyperscaling rules are modified above the upper critical dimension. It was shown [...] Read more.
In addition to the standard scaling rules relating critical exponents at second order transitions, hyperscaling rules involve the dimension of the model. It is well known that in canonical Ising models hyperscaling rules are modified above the upper critical dimension. It was shown by M. Schwartz in 1991 that hyperscaling can also break down in Ising systems with quenched random interactions; Random Field Ising models, which are in this class, have been intensively studied. Here, numerical Ising Spin Glass data relating the scaling of the normalized Binder cumulant to that of the reduced correlation length are presented for dimensions 3, 4, 5, and 7. Hyperscaling is clearly violated in dimensions 3 and 4, as well as above the upper critical dimension D = 6 . Estimates are obtained for the “violation of hyperscaling exponent” values in the various models. Full article
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Figure 1

Figure 1
<p>(Color on line) Dimension 3 simple cubic Ising model. Normalized Binder cumulant <math display="inline"><semantics> <mrow> <msup> <mi>L</mi> <mn>3</mn> </msup> <mi>g</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> against reduced correlation length to the power 3, <math display="inline"><semantics> <mrow> <mn>1</mn> <mo>/</mo> <msup> <mrow> <mo>(</mo> <mi>ξ</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> <mo>/</mo> <msup> <mi>β</mi> <mrow> <mn>1</mn> <mo>/</mo> <mn>2</mn> </mrow> </msup> <mo>)</mo> </mrow> <mn>3</mn> </msup> </mrow> </semantics></math>. Sample sizes: <math display="inline"><semantics> <mrow> <mi>L</mi> <mo>=</mo> <mn>32</mn> </mrow> </semantics></math>, 24, 16, 8, 6 (top to bottom). Blue straight line: slope <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>1</mn> <mo>.</mo> <mn>00</mn> </mrow> </semantics></math>. In this and all following figures each line for fixed <span class="html-italic">L</span> begins to bend over towards horizontal when it leaves the ThL regime <math display="inline"><semantics> <mrow> <mi>L</mi> <mo>&gt;</mo> <mo>&gt;</mo> <mi>ξ</mi> <mo>(</mo> <mi>β</mi> <mo>)</mo> </mrow> </semantics></math>.</p>
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<p>(Color on line) Dimension 3 simple cubic bimodal ISG model. Normalized Binder cumulant <math display="inline"><semantics> <mrow> <msup> <mi>L</mi> <mn>3</mn> </msup> <mi>g</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> against reduced correlation length to the power 3, <math display="inline"><semantics> <mrow> <mn>1</mn> <mo>/</mo> <msup> <mrow> <mo>(</mo> <mi>ξ</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> <mo>/</mo> <mi>β</mi> <mo>)</mo> </mrow> <mn>3</mn> </msup> </mrow> </semantics></math>. Sample sizes: <math display="inline"><semantics> <mrow> <mi>L</mi> <mo>=</mo> <mn>32</mn> </mrow> </semantics></math>, 24, 16, 12, 8, 6 (top to bottom). Green straight line: slope <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>1</mn> <mo>.</mo> <mn>27</mn> </mrow> </semantics></math>.</p>
Full article ">Figure 3
<p>(Color on line) Dimension 3 simple cubic Gaussian ISG model. Normalized Binder cumulant <math display="inline"><semantics> <mrow> <msup> <mi>L</mi> <mn>3</mn> </msup> <mi>g</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> against reduced correlation length to the power 3, <math display="inline"><semantics> <mrow> <mn>1</mn> <mo>/</mo> <msup> <mrow> <mo>(</mo> <mi>ξ</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> <mo>/</mo> <mi>β</mi> <mo>)</mo> </mrow> <mn>3</mn> </msup> </mrow> </semantics></math>. Sample sizes: <math display="inline"><semantics> <mrow> <mi>L</mi> <mo>=</mo> <mn>32</mn> </mrow> </semantics></math>, 24, 16, 12, 8, 6 (top to bottom). Green straight line: slope <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>1</mn> <mo>.</mo> <mn>23</mn> </mrow> </semantics></math>.</p>
Full article ">Figure 4
<p>(Color on line) Dimension 3 face-centered cubic Laplacian ISG model. Normalized Binder cumulant <math display="inline"><semantics> <mrow> <msup> <mi>L</mi> <mn>3</mn> </msup> <mi>g</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> against reduced correlation length to the power 3, <math display="inline"><semantics> <mrow> <mn>1</mn> <mo>/</mo> <msup> <mrow> <mo>(</mo> <mi>ξ</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> <mo>/</mo> <mi>β</mi> <mo>)</mo> </mrow> <mn>3</mn> </msup> </mrow> </semantics></math>. Sample sizes: <math display="inline"><semantics> <mrow> <mi>L</mi> <mo>=</mo> <mn>28</mn> </mrow> </semantics></math>, 24, 20, 18, 16, 14, 12, 10, 8, 6 (top to bottom). Green straight line: slope <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>1</mn> <mo>.</mo> <mn>27</mn> </mrow> </semantics></math>.</p>
Full article ">Figure 5
<p>(Color on line) Dimension 4 hypercubic bimodal ISG model. Normalized Binder cumulant <math display="inline"><semantics> <mrow> <msup> <mi>L</mi> <mn>4</mn> </msup> <mi>g</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> against reduced correlation length to the power 4, <math display="inline"><semantics> <mrow> <mn>1</mn> <mo>/</mo> <msup> <mrow> <mo>(</mo> <mi>ξ</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> <mo>/</mo> <mi>β</mi> <mo>)</mo> </mrow> <mn>4</mn> </msup> </mrow> </semantics></math>. Sample sizes: <math display="inline"><semantics> <mrow> <mi>L</mi> <mo>=</mo> <mn>14</mn> </mrow> </semantics></math>, 12, 10, 8, 6, 4 (top to bottom). Green straight line: slope <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>1</mn> <mo>.</mo> <mn>12</mn> </mrow> </semantics></math>.</p>
Full article ">Figure 6
<p>(Color on line) Dimension 4 hypercubic Gaussian ISG model. Normalized Binder cumulant <math display="inline"><semantics> <mrow> <msup> <mi>L</mi> <mn>4</mn> </msup> <mi>g</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> against reduced correlation length to the power 4, <math display="inline"><semantics> <mrow> <mn>1</mn> <mo>/</mo> <msup> <mrow> <mo>(</mo> <mi>ξ</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> <mo>/</mo> <mi>β</mi> <mo>)</mo> </mrow> <mn>4</mn> </msup> </mrow> </semantics></math>. Sample sizes: <math display="inline"><semantics> <mrow> <mi>L</mi> <mo>=</mo> <mn>14</mn> </mrow> </semantics></math>, 12, 10, 8, 6, 4 (top to bottom). Green straight line: slope <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>1</mn> <mo>.</mo> <mn>13</mn> </mrow> </semantics></math>.</p>
Full article ">Figure 7
<p>(Color on line) Dimension 5 hypercubic bimodal ISG model. Normalized Binder cumulant <math display="inline"><semantics> <mrow> <msup> <mi>L</mi> <mn>5</mn> </msup> <mi>g</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> against reduced correlation length to the power 5, <math display="inline"><semantics> <mrow> <mn>1</mn> <mo>/</mo> <msup> <mrow> <mo>(</mo> <mi>ξ</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> <mo>/</mo> <mi>β</mi> <mo>)</mo> </mrow> <mn>5</mn> </msup> </mrow> </semantics></math>. Sample sizes: <math display="inline"><semantics> <mrow> <mi>L</mi> <mo>=</mo> <mn>10</mn> </mrow> </semantics></math>, 8, 6, 4 (top to bottom). Green straight line: slope <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>1</mn> <mo>.</mo> <mn>00</mn> </mrow> </semantics></math>.</p>
Full article ">Figure 8
<p>(Color on line) Dimension 5 hypercubic Gaussian ISG model. Normalized Binder cumulant <math display="inline"><semantics> <mrow> <msup> <mi>L</mi> <mn>5</mn> </msup> <mi>g</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> against reduced correlation length to the power 5, <math display="inline"><semantics> <mrow> <mn>1</mn> <mo>/</mo> <msup> <mrow> <mo>(</mo> <mi>ξ</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> <mo>/</mo> <mi>β</mi> <mo>)</mo> </mrow> <mn>5</mn> </msup> </mrow> </semantics></math>. Sample sizes: <math display="inline"><semantics> <mrow> <mi>L</mi> <mo>=</mo> <mn>10</mn> </mrow> </semantics></math>, 8, 6, 4 (top to bottom). Green straight line: slope <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>1</mn> <mo>.</mo> <mn>00</mn> </mrow> </semantics></math>.</p>
Full article ">Figure 9
<p>(Color on line) Dimension 7 hypercubic bimodal ISG model. Normalized Binder cumulant <math display="inline"><semantics> <mrow> <msup> <mi>L</mi> <mn>7</mn> </msup> <mi>g</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> against reduced correlation length to the power 7, <math display="inline"><semantics> <mrow> <mn>1</mn> <mo>/</mo> <msup> <mrow> <mo>(</mo> <mi>ξ</mi> <mrow> <mo>(</mo> <mi>β</mi> <mo>,</mo> <mi>L</mi> <mo>)</mo> </mrow> <mo>/</mo> <mi>β</mi> <mo>)</mo> </mrow> <mn>7</mn> </msup> </mrow> </semantics></math>. Sample sizes: <math display="inline"><semantics> <mrow> <mi>L</mi> <mo>=</mo> <mn>7</mn> </mrow> </semantics></math>, 6, 5, 4, 3 (top to bottom). Green straight line: slope <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>0</mn> <mo>.</mo> <mn>75</mn> </mrow> </semantics></math>.</p>
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9 pages, 306 KiB  
Article
Kinetic Models of Discrete Opinion Dynamics on Directed Barabási–Albert Networks
by F. Welington S. Lima and J. A. Plascak
Entropy 2019, 21(10), 942; https://doi.org/10.3390/e21100942 - 26 Sep 2019
Cited by 12 | Viewed by 2554
Abstract
Kinetic models of discrete opinion dynamics are studied on directed Barabási–Albert networks by using extensive Monte Carlo simulations. A continuous phase transition has been found in this system. The critical values of the noise parameter are obtained for several values of the connectivity [...] Read more.
Kinetic models of discrete opinion dynamics are studied on directed Barabási–Albert networks by using extensive Monte Carlo simulations. A continuous phase transition has been found in this system. The critical values of the noise parameter are obtained for several values of the connectivity of these directed networks. In addition, the ratio of the critical exponents of the order parameter and the corresponding susceptibility to the correlation length have also been computed. It is noticed that the kinetic model and the majority-vote model on these directed Barabási–Albert networks are in the same universality class. Full article
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Figure 1
<p>Fourth-order Binder cumulant <math display="inline"><semantics> <msub> <mi>U</mi> <mn>4</mn> </msub> </semantics></math> as a function of the disorder parameter <span class="html-italic">p</span> for several number of nodes <span class="html-italic">N</span> and two connectivity numbers: <math display="inline"><semantics> <mrow> <mi>z</mi> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math> (<b>a</b>) and <math display="inline"><semantics> <mrow> <mi>z</mi> <mo>=</mo> <mn>100</mn> </mrow> </semantics></math> (<b>b</b>). The vertical arrows indicate the corresponding estimate of <math display="inline"><semantics> <msub> <mi>p</mi> <mi>c</mi> </msub> </semantics></math>, which is given in <a href="#entropy-21-00942-t001" class="html-table">Table 1</a>. For clarity, only the general trend of the cumulant behavior is shown without the error bars.</p>
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<p>(Color on-line). Ln-ln plot of the average opinion at the estimated critical disorder <math display="inline"><semantics> <mrow> <mi>O</mi> <mo stretchy="false">(</mo> <msub> <mi>p</mi> <mi>c</mi> </msub> <mo stretchy="false">)</mo> </mrow> </semantics></math> as a function of the number of nodes <span class="html-italic">N</span> for different connectivities <span class="html-italic">z</span>. The lines are the best linear fit with the slope being the critical exponent ratio <math display="inline"><semantics> <mrow> <mi>β</mi> <mo stretchy="false">/</mo> <mi>ν</mi> </mrow> </semantics></math>. Please note that the shown error bars are smaller than the symbol sizes.</p>
Full article ">Figure 3
<p>Ln-ln plot of the susceptibility <math display="inline"><semantics> <mrow> <mi>χ</mi> <mo stretchy="false">(</mo> <msub> <mi>p</mi> <mi>c</mi> </msub> <mo stretchy="false">)</mo> </mrow> </semantics></math> at the estimated <math display="inline"><semantics> <msub> <mi>p</mi> <mi>c</mi> </msub> </semantics></math> as a function of the number of nodes <span class="html-italic">N</span> for different connectivities <span class="html-italic">z</span>. The lines are the best linear fit with the slope being the critical exponent ratio <math display="inline"><semantics> <mrow> <mi>γ</mi> <mo stretchy="false">/</mo> <mi>ν</mi> </mrow> </semantics></math>. The displayed error bars are smaller than the symbol sizes.</p>
Full article ">Figure 4
<p>Ln-ln plot of the susceptibility <math display="inline"><semantics> <mi>χ</mi> </semantics></math> as a function of <span class="html-italic">N</span> for several values of the connectivity <span class="html-italic">z</span>. Open symbols correspond to the susceptibility evaluated at <math display="inline"><semantics> <msub> <mi>p</mi> <mi>c</mi> </msub> </semantics></math>, while full symbols are evaluated at the maximum value of the susceptibility <math display="inline"><semantics> <msub> <mi>p</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> </semantics></math>. The lines are linear fits with the corresponding exponents ratio given in <a href="#entropy-21-00942-t001" class="html-table">Table 1</a>.</p>
Full article ">Figure 5
<p>Ln-ln plot of the maximum of the susceptibility <math display="inline"><semantics> <msub> <mi>χ</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> </semantics></math> at <math display="inline"><semantics> <msub> <mi>p</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> </semantics></math> as a function of the number of nodes <span class="html-italic">N</span> for different connectivities <span class="html-italic">z</span>. The lines are the best linear fit with the slope giving the critical exponent ratio <math display="inline"><semantics> <mrow> <mi>γ</mi> <mo stretchy="false">/</mo> <mi>ν</mi> </mrow> </semantics></math>.</p>
Full article ">Figure 6
<p>Critical exponents ratio <math display="inline"><semantics> <mrow> <mi>β</mi> <mo stretchy="false">/</mo> <mi>ν</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>γ</mi> <mo stretchy="false">/</mo> <mi>ν</mi> </mrow> </semantics></math>, and half value of the effective dimension <math display="inline"><semantics> <msub> <mi>D</mi> <mrow> <mi>e</mi> <mi>f</mi> <mi>f</mi> </mrow> </msub> </semantics></math> as a function of the connectivity <span class="html-italic">z</span>. Full symbols correspond to the present BCS model, and open symbols to the MVM [<a href="#B8-entropy-21-00942" class="html-bibr">8</a>], both on the same DBAN. Full and dashed lines are only guide to the eyes.</p>
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<p>Phase diagram in the connectivity <span class="html-italic">z</span> and disorder <span class="html-italic">p</span> parameters plane for the BCS model (circles) and MVM (squares) on the DBAN.</p>
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16 pages, 291 KiB  
Article
Universality and Exact Finite-Size Corrections for Spanning Trees on Cobweb and Fan Networks
by Nickolay Izmailian and Ralph Kenna
Entropy 2019, 21(9), 895; https://doi.org/10.3390/e21090895 - 15 Sep 2019
Viewed by 2481
Abstract
The concept of universality is a cornerstone of theories of critical phenomena. It is very well understood in most systems, especially in the thermodynamic limit. Finite-size systems present additional challenges. Even in low dimensions, universality of the edge and corner contributions to free [...] Read more.
The concept of universality is a cornerstone of theories of critical phenomena. It is very well understood in most systems, especially in the thermodynamic limit. Finite-size systems present additional challenges. Even in low dimensions, universality of the edge and corner contributions to free energies and response functions is less investigated and less well understood. In particular, the question arises of how universality is maintained in correction-to-scaling in systems of the same universality class but with very different corner geometries. Two-dimensional geometries deliver the simplest such examples that can be constructed with and without corners. To investigate how the presence and absence of corners manifest universality, we analyze the spanning tree generating function on two different finite systems, namely the cobweb and fan networks. The corner free energies of these configurations have stimulated significant interest precisely because of expectations regarding their universal properties and we address how this can be delivered given that the finite-size cobweb has no corners while the fan has four. To answer, we appeal to the Ivashkevich–Izmailian–Hu approach which unifies the generating functions of distinct networks in terms of a single partition function with twisted boundary conditions. This unified approach shows that the contributions to the individual corner free energies of the fan network sum to zero so that it precisely matches that of the web. It therefore also matches conformal theory (in which the central charge is found to be c = 2 ) and finite-size scaling predictions. Correspondence in each case with results established by alternative means for both networks verifies the soundness of the Ivashkevich–Izmailian–Hu algorithm. Its broad range of usefulness is demonstrated by its application to hitherto unsolved problems—namely the exact asymptotic expansions of the logarithms of the generating functions and the conformal partition functions for fan and cobweb geometries. We also investigate strip geometries, again confirming the predictions of conformal field theory. Thus, the resolution of a universality puzzle demonstrates the power of the algorithm and opens up new applications in the future. Full article
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Figure 1
<p>An <math display="inline"><semantics> <mrow> <mi>M</mi> <mo>×</mo> <mi>N</mi> </mrow> </semantics></math> cobweb network with <math display="inline"><semantics> <mrow> <mi>M</mi> <mo>=</mo> <mn>3</mn> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>N</mi> <mo>=</mo> <mn>8</mn> </mrow> </semantics></math> (<b>a</b>). An <math display="inline"><semantics> <mrow> <mi>M</mi> <mo>×</mo> <mi>N</mi> </mrow> </semantics></math> fan network with <math display="inline"><semantics> <mrow> <mi>M</mi> <mo>=</mo> <mn>3</mn> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>N</mi> <mo>=</mo> <mn>7</mn> </mrow> </semantics></math> (<b>b</b>). The weights <span class="html-italic">x</span> and <span class="html-italic">y</span> are assigned to the bonds in circular and radial directions, respectively. The cobweb network can be considered as a cylinder, where all sites on the one boundary are connected to an external common site, which is denoted by 0, while the fan network can be considered as a plane rectangular lattice, where all sites on one of four boundaries are connected to an external common site.</p>
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