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[[File:Sandpile identity 300x205.png|upright=1.25|thumb|The identity element of the sandpile group of a rectangular grid. Yellow pixels correspond to vertices carrying three particles, lilac to two particles, green to one, and black to zero.]]
[[File:Sandpile identity 300x205.png|upright=1.25|thumb|The identity element of the sandpile group of a rectangular grid. Yellow pixels correspond to vertices carrying three particles, lilac to two particles, green to one, and black to zero.]]
[[文件：沙堆身份300x205.png |直立=1.25 |拇指|矩形网格沙堆群的标识元素。黄色像素对应三个粒子的顶点，淡紫色代表两个粒子，绿色表示一个，黑色表示零。]]
[[文件：沙堆识别300x205.png |直立=1.25 |拇指|矩形网格沙堆群的标识元素。黄色像素对应三个粒子的顶点，淡紫色代表两个粒子，绿色表示一个，黑色表示零。]]
The identity element of the sandpile group of a rectangular grid. Yellow pixels correspond to vertices carrying three particles, lilac to two particles, green to one, and black to zero.
The identity element of the sandpile group of a rectangular grid. Yellow pixels correspond to vertices carrying three particles, lilac to two particles, green to one, and black to zero.
The sandpile model is a cellular automaton originally defined on a N\times M rectangular grid (checkerboard) \Gamma\subset\mathbb{Z}^2 of the standard square lattice \mathbb{Z}^2.
The sandpile model is a cellular automaton originally defined on a N\times M rectangular grid (checkerboard) \Gamma\subset\mathbb{Z}^2 of the standard square lattice \mathbb{Z}^2.
'''<font color="#ff8000"> 沙堆模型Sandpile model</font>'''是一个最初定义在 N\times M矩形网格(棋盘格) Gamma 子集 mathbb { z } ^ 2的标准正方形格子数学{ z } ^ 2上的l细胞自动机模型。
| pages = 381–384
| pages = 381–384
Choose a random vertex (x_i,y_i)\in\Gamma according to some probability distribution (usually uniform).
Choose a random vertex (x_i,y_i)\in\Gamma according to some probability distribution (usually uniform).
根据一些概率分布(通常是均匀的)选择一个随机顶点 (x_i,y_i)\in\Gamma。
The sandpile model is a [[cellular automaton]] originally defined on a <math>N\times M</math> rectangular grid (''checkerboard'') <math>\Gamma\subset\mathbb{Z}^2</math> of the [[Square lattice|standard square lattice]] <math>\mathbb{Z}^2</math>.
The sandpile model is a [[cellular automaton]] originally defined on a <math>N\times M</math> rectangular grid (''checkerboard'') <math>\Gamma\subset\mathbb{Z}^2</math> of the [[Square lattice|standard square lattice]] <math>\mathbb{Z}^2</math>.
沙堆模型是一个[[元胞自动机]]最初定义在一个<math>N\times M</math>矩形网格（“棋盘格”）<math>\Gamma\subset\mathbb{Z}^2</math>[[正方形格|标准正方形格]]<math>\mathbb{Z}^2</math>
沙堆模型是一个[[元胞自动机]]最初定义在一个<math>N\times M</math>矩形网格（“棋盘格”）<math>\Gamma\subset\mathbb{Z}^2</math>[[正方形格|标准正方形格]]<math>\mathbb{Z}^2</math>
The definition of the sandpile model given above for finite rectangular grids \Gamma\subset\mathbb{Z}^2 of the standard square lattice \mathbb{Z}^2 can then be seen as a special case of this definition: consider the graph G=(V,E) which is obtained from \Gamma by adding an additional vertex, the sink, and by drawing additional edges from the sink to every boundary vertex of \Gamma such that the degree of every non-sink vertex of G is four. In this manner, also sandpile models on non-rectangular grids of the standard square lattice (or of any other lattice) can be defined: Intersect some bounded subset S of \mathbb{R}^2 with \mathbb{Z}^2. Contract every edge of \mathbb{Z}^2 whose two endpoints are not in S\cap\mathbb{Z}^2. The single remaining vertex outside of S\cap\mathbb{Z}^2 then constitutes the sink of the resulting sandpile graph.
The definition of the sandpile model given above for finite rectangular grids \Gamma\subset\mathbb{Z}^2 of the standard square lattice \mathbb{Z}^2 can then be seen as a special case of this definition: consider the graph G=(V,E) which is obtained from \Gamma by adding an additional vertex, the sink, and by drawing additional edges from the sink to every boundary vertex of \Gamma such that the degree of every non-sink vertex of G is four. In this manner, also sandpile models on non-rectangular grids of the standard square lattice (or of any other lattice) can be defined: Intersect some bounded subset S of \mathbb{R}^2 with \mathbb{Z}^2. Contract every edge of \mathbb{Z}^2 whose two endpoints are not in S\cap\mathbb{Z}^2. The single remaining vertex outside of S\cap\mathbb{Z}^2 then constitutes the sink of the resulting sandpile graph.
上面给出的标准方格点阵\mathbb{Z}^2的有限矩形网格\Gamma\subset\mathbb{Z}^2的定义可以看作是这个定义的一个特例：考虑图G=（V，E），它是通过添加一个额外的顶点'''<font color="#ff8000"> 汇Sink</font>'''从Gamma获得的，并通过从汇点到每个边界顶点绘制附加边，使得G的每个非汇顶点的阶数为4。以这种方式，也可以定义标准正方形格（或任何其他格点）的非矩形网格上的沙堆模型：将\mathbb{R}^2的一些有界子集与\mathbb{Z}^2相交。收缩\mathbb{Z}^2的每条边，其两个端点不在S\cap\mathbb{Z}^2中。S\cap\mathbb{Z}^2之外的一个剩余顶点构成了结果沙堆图的汇。
The dynamics of the automaton at iteration <math>i\in\mathbb{N}</math> are then defined as follows:
The dynamics of the automaton at iteration <math>i\in\mathbb{N}</math> are then defined as follows:
# Choose a random vertex <math>(x_i,y_i)\in\Gamma</math> according to some probability distribution (usually uniform).
# Choose a random vertex <math>(x_i,y_i)\in\Gamma</math> according to some probability distribution (usually uniform).
#根据某种概率分布（通常是均匀的），选择一个随机顶点（x_i，y_i）\in\Gamma</math>。
#根据某种概率分布（通常是均匀的），选择一个随机顶点<math>(x_i,y_i)\in\Gamma</math>。
In the dynamics of the sandpile automaton defined above, some stable configurations (0\leq z(v)<4 for all v\in G\setminus\{s\}) appear infinitely often, while others can only appear a finite number of times (if at all). The former are referred to as recurrent configurations, while the latter are referred to as transient configurations. The recurrent configurations thereby consist of all stable non-negative configurations which can be reached from any other stable configuration by repeatedly adding grains of sand to vertices and toppling. It is easy to see that the minimally stable configuration z_m, where every vertex carries z_m(v)=deg(v)-1 grains of sand, is reachable from any other stable configuration (add deg(v)-z(v)-1\geq 0 grains to every vertex). Thus, equivalently, the recurrent configurations are exactly those configurations which can be reached from the minimally stable configuration by only adding grains of sand and stabilizing.
In the dynamics of the sandpile automaton defined above, some stable configurations (0\leq z(v)<4 for all v\in G\setminus\{s\}) appear infinitely often, while others can only appear a finite number of times (if at all). The former are referred to as recurrent configurations, while the latter are referred to as transient configurations. The recurrent configurations thereby consist of all stable non-negative configurations which can be reached from any other stable configuration by repeatedly adding grains of sand to vertices and toppling. It is easy to see that the minimally stable configuration z_m, where every vertex carries z_m(v)=deg(v)-1 grains of sand, is reachable from any other stable configuration (add deg(v)-z(v)-1\geq 0 grains to every vertex). Thus, equivalently, the recurrent configurations are exactly those configurations which can be reached from the minimally stable configuration by only adding grains of sand and stabilizing.
# If all vertices are ''stable'', i.e. <math>z_i(x,y)<4</math> for all <math>(x,y)\in\Gamma</math>, also the configuration <math>z_i</math> is said to be stable. In this case, continue with the next iteration.
# If all vertices are ''stable'', i.e. <math>z_i(x,y)<4</math> for all <math>(x,y)\in\Gamma</math>, also the configuration <math>z_i</math> is said to be stable. In this case, continue with the next iteration.
#如果所有顶点都是“稳定”的，即<math>z_i（x，y）<4</math>对于Gamma</math>中的所有<math>（x，y）<4</math>，那么配置<math>z酏i</math>也被称为稳定的。在这种情况下，继续下一个迭代。
#如果所有顶点都是“稳定”的，即<math>z_i（x，y）<4</math>对于Gamma</math>中的所有<math>（x，y）<4</math>，那么配置<math>z_i</math>也被称为稳定的。在这种情况下，继续下一个迭代。
Not every non-negative stable configuration is recurrent. For example, in every sandpile model on a graph consisting of at least two connected non-sink vertices, every stable configuration where both vertices carry zero grains of sand is non-recurrent. To prove this, first note that the addition of grains of sand can only increase the total number of grains carried by the two vertices together. To reach a configuration where both vertices carry zero particles from a configuration where this is not the case thus necessarily involves steps where at least one of the two vertices is toppled. Consider the last one of these steps. In this step, one of the two vertices has to topple last. Since toppling transfers a grain of sand to every neighboring vertex, this implies that the total number of grains carried by both vertices together cannot be lower than one, which concludes the proof.
Not every non-negative stable configuration is recurrent. For example, in every sandpile model on a graph consisting of at least two connected non-sink vertices, every stable configuration where both vertices carry zero grains of sand is non-recurrent. To prove this, first note that the addition of grains of sand can only increase the total number of grains carried by the two vertices together. To reach a configuration where both vertices carry zero particles from a configuration where this is not the case thus necessarily involves steps where at least one of the two vertices is toppled. Consider the last one of these steps. In this step, one of the two vertices has to topple last. Since toppling transfers a grain of sand to every neighboring vertex, this implies that the total number of grains carried by both vertices together cannot be lower than one, which concludes the proof.
# Due to the redistribution of grains, the toppling of one vertex can render other vertices unstable. Thus, repeat the toppling procedure until all vertices of <math>z_i</math> eventually become stable and continue with the next iteration.
# Due to the redistribution of grains, the toppling of one vertex can render other vertices unstable. Thus, repeat the toppling procedure until all vertices of <math>z_i</math> eventually become stable and continue with the next iteration.
#由于晶粒的重新分布，一个顶点的倾倒会使其他顶点变得不稳定。因此，重复倾倒过程，直到<math>züi</math>的所有顶点最终变得稳定，并继续下一个迭代。
Given a configuration z, z(v)\in\mathbb{N}_0 for all v\in G\setminus\{s\}, toppling unstable non-sink vertices on a finite connected graph until no unstable non-sink vertex remains leads to a unique stable configuration z^\circ, which is called the stabilization of z. Given two stable configurations z and w, we can define the operation z*w \to (z+w)^\circ, corresponding to the vertex-wise addition of grains followed by the stabilization of the resulting sandpile.
给定一个配置z，z（v）in\mathbb{N}0，对于所有的v\in G\setminus\{s\}，在有限连通图上倾倒不稳定的'''<font color="#ff8000"> 非汇顶点Non-sink vertices</font>'''，直到没有不稳定的非汇顶点存在，从而得到一个唯一的稳定配置z^环，这就是z的稳定化。给定两个稳定的z和w配置，我们可以定义z*w\to（z+w）^ circ，对应于在顶点方向上添加颗粒，然后稳定得到的沙堆。
The toppling of several vertices during one iteration is referred to as an ''avalanche''. Every avalanche is guaranteed to eventually stop, i.e. after a finite number of topplings some stable configuration is reached such that the automaton is well defined. Moreover, although there will often be many possible choices for the order in which to topple vertices, the final stable configuration does not depend on the chosen order; this is one sense in which the sandpile is [[Abelian group|''abelian'']]. Similarly, the number of times each vertex topples during each iteration is also independent of the choice of toppling order.
The toppling of several vertices during one iteration is referred to as an ''avalanche''. Every avalanche is guaranteed to eventually stop, i.e. after a finite number of topplings some stable configuration is reached such that the automaton is well defined. Moreover, although there will often be many possible choices for the order in which to topple vertices, the final stable configuration does not depend on the chosen order; this is one sense in which the sandpile is [[Abelian group|''abelian'']]. Similarly, the number of times each vertex topples during each iteration is also independent of the choice of toppling order.
在一次迭代过程中，一个顶点被称为“一个顶点的崩塌”。每一次雪崩都保证最终停止，也就是说，在有限数量的倾覆之后，达到某种稳定的配置，从而使自动机得到很好的定义。此外，虽然通常会有许多可能的选择，以何种顺序推翻顶点，最终的稳定配置并不取决于所选择的顺序；这一种意义上的沙堆是[[阿贝尔群|阿贝尔''']]。同样，每个顶点在每次迭代过程中的倒转次数也与翻转顺序的选择无关。
Given an arbitrary but fixed ordering of the non-sink vertices, multiple toppling operations, which can e.g. occur during the stabilization of an unstable configuration, can be efficiently encoded by using the graph Laplacian \Delta=D-A, where D is the degree matrix and A is the adjacency matrix of the graph.
Given an arbitrary but fixed ordering of the non-sink vertices, multiple toppling operations, which can e.g. occur during the stabilization of an unstable configuration, can be efficiently encoded by using the graph Laplacian \Delta=D-A, where D is the degree matrix and A is the adjacency matrix of the graph.
给定非汇聚顶点的一个任意但固定的顺序，多个顶点采样操作，它可以。在不稳定配置的稳定化过程中，可以通过使用图 Laplacian Delta = d-a 有效地进行编码，其中 d 是度矩阵，a 是图的邻接矩阵。
给定非汇聚顶点的一个任意但固定的顺序，多个顶点采样操作，它可以。在不稳定配置的稳定化过程中，可以通过使用图 Laplacian Delta = d-a 有效地进行编码，其中 d 是度矩阵，a 是图的邻接矩阵。
==Definition (undirected finite multigraphs)==
==Definition (undirected finite multigraphs)定义（无向有限多图）==
Deleting the row and column of \Delta corresponding with the sink yields the reduced graph Laplacian \Delta'. Then, when starting with a configuration z and toppling each vertex v a total of \mathbf{x}(v)\in\mathbb{N}_0 times yields the configuration z-\Delta'\boldsymbol{\cdot}~\mathbf{x}, where \boldsymbol{\cdot} is the contraction product. Furthermore, if \mathbf{x} corresponds to the number of times each vertex is toppled during the stabilization of a given configuration z, then
Deleting the row and column of \Delta corresponding with the sink yields the reduced graph Laplacian \Delta'. Then, when starting with a configuration z and toppling each vertex v a total of \mathbf{x}(v)\in\mathbb{N}_0 times yields the configuration z-\Delta'\boldsymbol{\cdot}~\mathbf{x}, where \boldsymbol{\cdot} is the contraction product. Furthermore, if \mathbf{x} corresponds to the number of times each vertex is toppled during the stabilization of a given configuration z, then
To generalize the sandpile model from the rectangular grid of the standard square lattice to an arbitrary undirected finite multigraph <math>G=(V,E)</math> without loops, a special vertex <math>s\in V</math> called the ''sink'' is specified that is not allowed to topple. A ''configuration'' (state) of the model is then a function <math>z:V\setminus\{s\}\rightarrow\mathbb{N}_0</math> counting the non-negative number of grains on each non-sink vertex. A non-sink vertex <math>v\in V\setminus\{s\}</math> with
To generalize the sandpile model from the rectangular grid of the standard square lattice to an arbitrary undirected finite multigraph <math>G=(V,E)</math> without loops, a special vertex <math>s\in V</math> called the ''sink'' is specified that is not allowed to topple. A ''configuration'' (state) of the model is then a function <math>z:V\setminus\{s\}\rightarrow\mathbb{N}_0</math> counting the non-negative number of grains on each non-sink vertex. A non-sink vertex <math>v\in V\setminus\{s\}</math> with
为了将沙堆模型从标准方格的矩形网格推广到任意无向有限多图，在V</math>中指定了一个称为“sink”的特殊顶点，称为“sink”。模型的“配置”（状态）就是一个函数<math>z:V\setminus\{s\}\rightarrow\mathbb{N}u0</math>计算每个非汇顶点上的非负晶粒数。<math>v\in V\setminus\{s\}</math> 中的非汇顶点
z^\circ=z-\Delta'\boldsymbol{\cdot}~\mathbf{x}
z^\circ=z-\Delta'\boldsymbol{\cdot}~\mathbf{x}
:<math>z(v)\geq \deg(v)</math>
:<math>z(v)\geq \deg(v)</math>
In this case, \mathbf{x} is referred to as the toppling or odometer function (of the stabilization of z).
In this case, \mathbf{x} is referred to as the toppling or odometer function (of the stabilization of z).
在这种情况下，\mathbf{x}被称为倾斜或里程计函数(表示 z 的稳定性)。
is unstable; it can be toppled, which sends one of its grains to each of its (non-sink) neighbors:
is unstable; it can be toppled, which sends one of its grains to each of its (non-sink) neighbors:
是不稳定的；它可以被推翻，这会将它的一个颗粒发送给它的每个（非下沉）邻居：
Under the operation *, the set of recurrent configurations forms an abelian group isomorphic to the cokernel of the reduced graph Laplacian \Delta', i.e. to \mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta', whereby n denotes the number of vertices (including the sink). More generally, the set of stable configurations (transient and recurrent) forms a commutative monoid under the operation *. The minimal ideal of this monoid is then isomorphic to the group of recurrent configurations.
Under the operation *, the set of recurrent configurations forms an abelian group isomorphic to the cokernel of the reduced graph Laplacian \Delta', i.e. to \mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta', whereby n denotes the number of vertices (including the sink). More generally, the set of stable configurations (transient and recurrent) forms a commutative monoid under the operation *. The minimal ideal of this monoid is then isomorphic to the group of recurrent configurations.
在* 运算下，递归构形的集合构成一个同构于约化图 laplace Delta’上核的阿贝尔群，即同构于约化图 laplace Delta’的上核。对于 mathbf { z } ^ { n-1}/mathbf { z } ^ { n-1} Delta’ ，其中 n 表示顶点数(包括接收器)。更一般地说，稳定构型集(瞬态和回归)在*运算下形成'''<font color="#ff8000"> 交换幺半群Commutative monoid</font>'''。这个幺半群的极小理想于是同构于一组回归构型。
:<math>z(v) \to z(v) - \deg(v)</math>
:<math>z(v) \to z(v) - \deg(v)</math>
The group formed by the recurrent configurations, as well as the group \mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta' to which the former is isomorphic, is most commonly referred to as the sandpile group. Other common names for the same group are critical group, Jacobian group or (less often) Picard group. Note, however, that some authors only denote the group formed by the recurrent configurations as the sandpile group, while reserving the name Jacobian group or critical group for the (isomorphic) group defined by \mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta' (or for related isomorphic definitions). Finally, some authors use the name Picard group to refer to the direct product of the sandpile group and \mathbb{Z}, which naturally appears in a cellular automaton closely related to the sandpile model, referred to as the chip firing or dollar game.
The group formed by the recurrent configurations, as well as the group \mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta' to which the former is isomorphic, is most commonly referred to as the sandpile group. Other common names for the same group are critical group, Jacobian group or (less often) Picard group. Note, however, that some authors only denote the group formed by the recurrent configurations as the sandpile group, while reserving the name Jacobian group or critical group for the (isomorphic) group defined by \mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta' (or for related isomorphic definitions). Finally, some authors use the name Picard group to refer to the direct product of the sandpile group and \mathbb{Z}, which naturally appears in a cellular automaton closely related to the sandpile model, referred to as the chip firing or dollar game.
由回归构形形成的群，以及与之同构的群 mathbf { z } ^ { n-1}/mathbf { z } ^ { n-1} Delta’ ，通常称为沙堆群。相同群的其他公共名称有临界群、雅可比群或(少见) Picard 群。注意，有些作者只把由回归构形形成的群称为沙堆群，而把雅可比群或临界群保留为 mathbf { z } ^ { n-1}/mathbf { z } ^ { n-1} Delta’(或相关的同构定义)所定义的(同构)群。最后，一些作者使用 Picard group 来指代 sandpile group 和 mathbb { z }的直接产物，后者自然出现在与 sandpile 模型密切相关的细胞自动机中，被称为芯片点火或美元游戏。
由回归构形形成的群，以及与之同构的群 mathbf { z } ^ { n-1}/mathbf { z } ^ { n-1} Delta’ ，通常称为'''<font color="#ff8000"> 沙堆群Sandpile group</font>'''。相同群的其他公共名称有临界群、雅可比群或(少见) Picard 群。注意，有些作者只把由回归构形形成的群称为沙堆群，而把雅可比群或临界群保留为 mathbf { z } ^ { n-1}/mathbf { z } ^ { n-1} Delta’(或相关的同构定义)所定义的(同构)群。最后，一些作者使用 Picard group 来指代 sandpile group 和 mathbb { z }的直接产物，后者自然出现在与 sandpile 模型密切相关的细胞自动机中，被称为'''<font color="#ff8000"> 芯片点火或美元游戏Chip firing or Dollar game</font>'''。
The cellular automaton then progresses as before, i.e. by adding, in each iteration, one particle to a randomly chosen non-sink vertex and toppling until all vertices are stable.
The cellular automaton then progresses as before, i.e. by adding, in each iteration, one particle to a randomly chosen non-sink vertex and toppling until all vertices are stable.
然后细胞自动机像以前一样进行，即在每次迭代中，将一个粒子添加到随机选择的非汇顶点，然后翻转，直到所有顶点都稳定为止。
Given the isomorphisms stated above, the order of the sandpile group is the determinant of \Delta', which by the matrix tree theorem is the number of spanning trees of the graph.
Given the isomorphisms stated above, the order of the sandpile group is the determinant of \Delta', which by the matrix tree theorem is the number of spanning trees of the graph.
The definition of the sandpile model given above for finite rectangular grids <math>\Gamma\subset\mathbb{Z}^2</math> of the standard square lattice <math>\mathbb{Z}^2</math> can then be seen as a special case of this definition: consider the graph <math>G=(V,E)</math> which is obtained from <math>\Gamma</math> by adding an additional vertex, the sink, and by drawing additional edges from the sink to every boundary vertex of <math>\Gamma</math> such that the [[Degree (graph theory)|degree]] of every non-sink vertex of <math>G</math> is four. In this manner, also sandpile models on non-rectangular grids of the standard square lattice (or of any other lattice) can be defined: Intersect some bounded subset <math>S</math> of <math>\mathbb{R}^2</math> with <math>\mathbb{Z}^2</math>. [[Edge contraction|Contract every edge]] of <math>\mathbb{Z}^2</math> whose two endpoints are not in <math>S\cap\mathbb{Z}^2</math>. The single remaining vertex outside of <math>S\cap\mathbb{Z}^2</math> then constitutes the sink of the resulting sandpile graph.
The definition of the sandpile model given above for finite rectangular grids <math>\Gamma\subset\mathbb{Z}^2</math> of the standard square lattice <math>\mathbb{Z}^2</math> can then be seen as a special case of this definition: consider the graph <math>G=(V,E)</math> which is obtained from <math>\Gamma</math> by adding an additional vertex, the sink, and by drawing additional edges from the sink to every boundary vertex of <math>\Gamma</math> such that the [[Degree (graph theory)|degree]] of every non-sink vertex of <math>G</math> is four. In this manner, also sandpile models on non-rectangular grids of the standard square lattice (or of any other lattice) can be defined: Intersect some bounded subset <math>S</math> of <math>\mathbb{R}^2</math> with <math>\mathbb{Z}^2</math>. [[Edge contraction|Contract every edge]] of <math>\mathbb{Z}^2</math> whose two endpoints are not in <math>S\cap\mathbb{Z}^2</math>. The single remaining vertex outside of <math>S\cap\mathbb{Z}^2</math> then constitutes the sink of the resulting sandpile graph.
上面给出的沙堆模型对于标准方格的有限矩形网格<math>\Gamma\subset\mathbb{Z}^2</math>的定义可以看作是这个定义的一个特例：考虑图<math>G=（V，E）</math>，它是通过添加一个额外的顶点从<math>\Gamma</math>获得的，并通过从汇到<math>\Gamma</math>的每个边界顶点绘制附加边，使得<math>G</math>的每个非汇顶点的[[度（图论）|度]]为4。以这种方式，也可以定义标准正方形格（或任何其他格点）的非矩形网格上的沙堆模型：将<math>\mathbb{R}^2</math>的某些有界子集<math>与<math>\mathbb{Z}^2</math>相交。两个端点不在<math>S\cap\mathbb{Z}^2</math>中的[[Edge construction | Contract every Edge]]。在<math>S\cap\mathbb{Z}^2</math>之外的单个剩余顶点构成了结果沙堆图的汇点。
==Transient and recurrent configurations瞬态和反复配置==
==Transient and recurrent configurations==
The original interest behind the model stemmed from the fact that in simulations on lattices, it is attracted to its critical state, at which point the correlation length of the system and the correlation time of the system go to infinity, without any fine tuning of a system parameter. This contrasts with earlier examples of critical phenomena, such as the phase transitions between solid and liquid, or liquid and gas, where the critical point can only be reached by precise tuning (e.g., of temperature). Hence, in the sandpile model we can say that the criticality is self-organized.
The original interest behind the model stemmed from the fact that in simulations on lattices, it is attracted to its critical state, at which point the correlation length of the system and the correlation time of the system go to infinity, without any fine tuning of a system parameter. This contrasts with earlier examples of critical phenomena, such as the phase transitions between solid and liquid, or liquid and gas, where the critical point can only be reached by precise tuning (e.g., of temperature). Hence, in the sandpile model we can say that the criticality is self-organized.
In the dynamics of the sandpile automaton defined above, some stable configurations (<math>0\leq z(v)<4</math> for all <math>v\in G\setminus\{s\}</math>) appear infinitely often, while others can only appear a finite number of times (if at all). The former are referred to as ''recurrent configurations'', while the latter are referred to as ''transient configurations''. The recurrent configurations thereby consist of all stable non-negative configurations which can be reached from any other stable configuration by repeatedly adding grains of sand to vertices and toppling. It is easy to see that the ''minimally stable configuration'' <math>z_m</math>, where every vertex carries <math>z_m(v)=deg(v)-1</math> grains of sand, is reachable from any other stable configuration (add <math>deg(v)-z(v)-1\geq 0</math> grains to every vertex). Thus, equivalently, the recurrent configurations are exactly those configurations which can be reached from the minimally stable configuration by only adding grains of sand and stabilizing.
In the dynamics of the sandpile automaton defined above, some stable configurations (<math>0\leq z(v)<4</math> for all <math>v\in G\setminus\{s\}</math>) appear infinitely often, while others can only appear a finite number of times (if at all). The former are referred to as ''recurrent configurations'', while the latter are referred to as ''transient configurations''. The recurrent configurations thereby consist of all stable non-negative configurations which can be reached from any other stable configuration by repeatedly adding grains of sand to vertices and toppling. It is easy to see that the ''minimally stable configuration'' <math>z_m</math>, where every vertex carries <math>z_m(v)=deg(v)-1</math> grains of sand, is reachable from any other stable configuration (add <math>deg(v)-z(v)-1\geq 0</math> grains to every vertex). Thus, equivalently, the recurrent configurations are exactly those configurations which can be reached from the minimally stable configuration by only adding grains of sand and stabilizing.
在上面定义的沙堆自动机的动力学中，一些稳定的配置（<math>0\leq z（v）<4</math>for all<math>v\In G\setminus\{s\}</math>）经常无限次出现，而另一些则只能出现有限次（如果有的话）。前者被称为“重复配置”，而后者被称为“瞬态配置”。因此，周期性构形由所有稳定的非负构形组成，这些构形可以通过反复向顶点添加砂粒和倾倒而达到。很容易看出，“最小稳定配置”<math>zum</math>，其中每个顶点携带<math>zum（v）=deg（v）-1</math>沙粒，可从任何其他稳定配置（向每个顶点添加<math>deg（v）-z（v）-1\geq 0</math>颗粒）。因此，等效地说，周期性构型正是通过添加沙粒和稳定化就可以从最小稳定构型得到的构型。
Once the sandpile model reaches its critical state there is no correlation between the system's response to a perturbation and the details of a perturbation. Generally this means that dropping another grain of sand onto the pile may cause nothing to happen, or it may cause the entire pile to collapse in a massive slide. The model also displays 1/ƒ noise, a feature common to many complex systems in nature.
Once the sandpile model reaches its critical state there is no correlation between the system's response to a perturbation and the details of a perturbation. Generally this means that dropping another grain of sand onto the pile may cause nothing to happen, or it may cause the entire pile to collapse in a massive slide. The model also displays 1/ƒ noise, a feature common to many complex systems in nature.
Not every non-negative stable configuration is recurrent. For example, in every sandpile model on a graph consisting of at least two connected non-sink vertices, every stable configuration where both vertices carry zero grains of sand is non-recurrent. To prove this, first note that the addition of grains of sand can only increase the total number of grains carried by the two vertices together. To reach a configuration where both vertices carry zero particles from a configuration where this is not the case thus necessarily involves steps where at least one of the two vertices is toppled. Consider the last one of these steps. In this step, one of the two vertices has to topple last. Since toppling transfers a grain of sand to every neighboring vertex, this implies that the total number of grains carried by both vertices together cannot be lower than one, which concludes the proof.
Not every non-negative stable configuration is recurrent. For example, in every sandpile model on a graph consisting of at least two connected non-sink vertices, every stable configuration where both vertices carry zero grains of sand is non-recurrent. To prove this, first note that the addition of grains of sand can only increase the total number of grains carried by the two vertices together. To reach a configuration where both vertices carry zero particles from a configuration where this is not the case thus necessarily involves steps where at least one of the two vertices is toppled. Consider the last one of these steps. In this step, one of the two vertices has to topple last. Since toppling transfers a grain of sand to every neighboring vertex, this implies that the total number of grains carried by both vertices together cannot be lower than one, which concludes the proof.
不是每一个非负稳定组态都是重复的。例如，在由至少两个连通的非汇点组成的图上的每个沙堆模型中，每个顶点携带零粒沙子的稳定配置都是非递归的。为了证明这一点，首先要注意的是，添加砂粒只会增加两个顶点同时携带的颗粒总数。要达到两个顶点都携带零粒子的配置，而不是这样的配置，因此必须涉及两个顶点中至少一个被推翻的步骤。考虑以下最后一个步骤。在这个步骤中，两个顶点中的一个必须最后倾倒。由于倾倒将一粒沙子转移到每个相邻的顶点，这意味着两个顶点同时携带的沙粒总数不能少于一个，这就证明了这一点。
This model only displays critical behaviour in two or more dimensions. The sandpile model can be expressed in 1D; however, instead of evolving to its critical state, the 1D sandpile model instead reaches a minimally stable state where every lattice site goes toward the critical slope.
This model only displays critical behaviour in two or more dimensions. The sandpile model can be expressed in 1D; however, instead of evolving to its critical state, the 1D sandpile model instead reaches a minimally stable state where every lattice site goes toward the critical slope.
此模型仅在两个或多个维度中显示关键行为。沙堆模型可以用一维来表示; 然而，一维沙堆模型不是演化到临界状态，而是达到最小稳定状态，其中每个格点都朝向临界坡度。
此模型仅在两个或多个维度中显示关键行为。沙堆模型可以用一维来表示; 然而，一维沙堆模型不是演化到临界状态，而是达到最小稳定状态，其中每个格点都朝向临界坡度。
==Sandpile group==
==Sandpile group沙堆群==
Given a configuration <math>z</math>, <math>z(v)\in\mathbb{N}_0</math> for all <math>v\in G\setminus\{s\}</math>, toppling unstable non-sink vertices on a finite connected graph until no unstable non-sink vertex remains leads to a unique ''stable'' configuration <math>z^\circ</math>, which is called the ''stabilization'' of <math>z</math>. Given two stable configurations <math>z</math> and <math>w</math>, we can define the operation <math>z*w \to (z+w)^\circ</math>, corresponding to the vertex-wise addition of grains followed by the stabilization of the resulting sandpile.
Given a configuration <math>z</math>, <math>z(v)\in\mathbb{N}_0</math> for all <math>v\in G\setminus\{s\}</math>, toppling unstable non-sink vertices on a finite connected graph until no unstable non-sink vertex remains leads to a unique ''stable'' configuration <math>z^\circ</math>, which is called the ''stabilization'' of <math>z</math>. Given two stable configurations <math>z</math> and <math>w</math>, we can define the operation <math>z*w \to (z+w)^\circ</math>, corresponding to the vertex-wise addition of grains followed by the stabilization of the resulting sandpile.
给定一个配置<math>z</math>，<math>z（v）\in\mathbb{N}u 0</math>对于所有<math>v\in G\setminus\{s\}</math>，在有限连通图上翻转不稳定的非汇顶点，直到没有不稳定的非汇顶点保留，这将导致唯一的“稳定”配置<math>z^\circ</math>，这就是<math>z</math>的“稳定化”。给定两个稳定构型<math>z</math>和<math>w</math>，我们可以定义运算<math>z*w\ to（z+w）^\circ</math>，对应于颗粒的顶点方向相加，然后稳定得到的沙堆。
For two dimensions, the associated conformal field theory is suggested to be symplectic fermions with central charge c = −2.
For two dimensions, the associated conformal field theory is suggested to be symplectic fermions with central charge c = −2.
Given an arbitrary but fixed ordering of the non-sink vertices, multiple toppling operations, which can e.g. occur during the stabilization of an unstable configuration, can be efficiently encoded by using the [[Laplacian matrix|graph Laplacian]] <math>\Delta=D-A</math>, where <math>D</math> is the [[degree matrix]] and <math>A</math> is the [[adjacency matrix]] of the graph.
Given an arbitrary but fixed ordering of the non-sink vertices, multiple toppling operations, which can e.g. occur during the stabilization of an unstable configuration, can be efficiently encoded by using the [[Laplacian matrix|graph Laplacian]] <math>\Delta=D-A</math>, where <math>D</math> is the [[degree matrix]] and <math>A</math> is the [[adjacency matrix]] of the graph.
给定非汇顶点的任意但固定的顺序，可以通过使用[[拉普拉斯矩阵|图拉普拉斯]]<math>\Delta=D-A</math>高效地编码多个倾倒操作（例如，在稳定不稳定配置期间），其中<math>D</math>是图的[[度矩阵]]，<math>A</math>是图的[[邻接矩阵]]。
Deleting the row and column of <math>\Delta</math> corresponding with the sink yields the ''reduced graph Laplacian'' <math>\Delta'</math>. Then, when starting with a configuration <math>z</math> and toppling each vertex <math>v</math> a total of <math>\mathbf{x}(v)\in\mathbb{N}_0</math> times yields the configuration <math>z-\Delta'\boldsymbol{\cdot}~\mathbf{x}</math>, where <math>\boldsymbol{\cdot}</math> is the contraction product. Furthermore, if <math>\mathbf{x}</math> corresponds to the number of times each vertex is toppled during the stabilization of a given configuration <math>z</math>, then
Deleting the row and column of <math>\Delta</math> corresponding with the sink yields the ''reduced graph Laplacian'' <math>\Delta'</math>. Then, when starting with a configuration <math>z</math> and toppling each vertex <math>v</math> a total of <math>\mathbf{x}(v)\in\mathbb{N}_0</math> times yields the configuration <math>z-\Delta'\boldsymbol{\cdot}~\mathbf{x}</math>, where <math>\boldsymbol{\cdot}</math> is the contraction product. Furthermore, if <math>\mathbf{x}</math> corresponds to the number of times each vertex is toppled during the stabilization of a given configuration <math>z</math>, then
删除与sink相对应的<math>\Delta</math>的行和列将生成“reduced graph Laplacian”<math>\Delta'</math>。然后，当从一个配置<math>z</math>开始，并推翻每个顶点<math>v</math>时，总的<math>\mathbf{x}（v）\in\mathbb{N}u0</math>得到配置<math>z-\Delta'\boldsymbol{\cdot}~\mathbf{x}</math>，其中<math>\boldsymbol{\cdot}</math>是收缩积。此外，如果<math>\mathbf{x}</math>对应于给定配置稳定期间每个顶点被推翻的次数<math>z</math>，则
:<math>z^\circ=z-\Delta'\boldsymbol{\cdot}~\mathbf{x}</math>
:<math>z^\circ=z-\Delta'\boldsymbol{\cdot}~\mathbf{x}</math>
In this case, <math>\mathbf{x}</math> is referred to as the ''toppling'' or ''odometer function'' (of the stabilization of <math>z</math>).
In this case, <math>\mathbf{x}</math> is referred to as the ''toppling'' or ''odometer function'' (of the stabilization of <math>z</math>).
在这种情况下，<math>\mathbf{x}</math>被称为“倾倒”或“里程表函数”（稳定<math>z</math>）。
This can be formalized as follows. Call a sequence of topples legal if it only topples unstable vertices, and stabilizing if it results in a stable configuration. The standard way of stabilizing the sandpile is to find a maximal legal sequence; i.e., by toppling so long as it is possible. Such a sequence is obviously stabilizing, and the Abelian property of the sandpile is that all such sequences are equivalent up to permutation of the toppling order; that is, for any vertex v, the number of times v topples is the same in all legal stabilizing sequences. According to the least action principle, a minimal stabilizing sequence is also equivalent up to permutation of the toppling order to a legal (and still stabilizing) sequence. In particular, the configuration resulting from a minimal stabilizing sequence is the same as results from a maximal legal sequence.
This can be formalized as follows. Call a sequence of topples legal if it only topples unstable vertices, and stabilizing if it results in a stable configuration. The standard way of stabilizing the sandpile is to find a maximal legal sequence; i.e., by toppling so long as it is possible. Such a sequence is obviously stabilizing, and the Abelian property of the sandpile is that all such sequences are equivalent up to permutation of the toppling order; that is, for any vertex v, the number of times v topples is the same in all legal stabilizing sequences. According to the least action principle, a minimal stabilizing sequence is also equivalent up to permutation of the toppling order to a legal (and still stabilizing) sequence. In particular, the configuration resulting from a minimal stabilizing sequence is the same as results from a maximal legal sequence.
Under the operation <math>*</math>, the set of recurrent configurations forms an [[abelian group]] isomorphic to the cokernel of the reduced graph Laplacian <math>\Delta'</math>, i.e. to <math>\mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta'</math>, whereby <math>n</math> denotes the number of vertices (including the sink). More generally, the set of stable configurations (transient and recurrent) forms a [[commutative monoid]] under the operation <math>*</math>. The minimal [[Semigroup#Subsemigroups and ideals|ideal]] of this monoid is then isomorphic to the group of recurrent configurations.
Under the operation <math>*</math>, the set of recurrent configurations forms an [[abelian group]] isomorphic to the cokernel of the reduced graph Laplacian <math>\Delta'</math>, i.e. to <math>\mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta'</math>, whereby <math>n</math> denotes the number of vertices (including the sink). More generally, the set of stable configurations (transient and recurrent) forms a [[commutative monoid]] under the operation <math>*</math>. The minimal [[Semigroup#Subsemigroups and ideals|ideal]] of this monoid is then isomorphic to the group of recurrent configurations.
在运算<math>*</math>下，一组递归配置形成一个[[阿贝尔群]]同构于约化图Laplacian<math>\Delta'</math>的余核，即to<math>\mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta'</math>，其中<math>n</math>表示顶点数（包括汇）。更一般地说，在运算<math>*</math>下，稳定组态集（瞬态和递归）形成[[交换幺半群]]。这个幺半群的极小[[半群#子半群和理想|理想]]则同构于循环构形群。
More formally, if \mathbf{u} is a vector such that \mathbf{u}(v) is the number of times the vertex v topples during the stabilization (via the toppling of unstable vertices) of a chip configuration z, and \mathbf{n} is an integral vector (not necessarily non-negative) such that z-\mathbf{n}\Delta' is stable, then \mathbf{u}(v) \leq \mathbf{n}(v) for all vertices v.
More formally, if \mathbf{u} is a vector such that \mathbf{u}(v) is the number of times the vertex v topples during the stabilization (via the toppling of unstable vertices) of a chip configuration z, and \mathbf{n} is an integral vector (not necessarily non-negative) such that z-\mathbf{n}\Delta' is stable, then \mathbf{u}(v) \leq \mathbf{n}(v) for all vertices v.
The group formed by the recurrent configurations, as well as the group <math>\mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta'</math> to which the former is isomorphic, is most commonly referred to as the ''sandpile group''. Other common names for the same group are ''critical group'', ''Jacobian group'' or (less often) ''Picard group''. Note, however, that some authors only denote the group formed by the recurrent configurations as the sandpile group, while reserving the name Jacobian group or critical group for the (isomorphic) group defined by <math>\mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta'</math> (or for related isomorphic definitions). Finally, some authors use the name Picard group to refer to the direct product of the sandpile group and <math>\mathbb{Z}</math>, which naturally appears in a cellular automaton closely related to the sandpile model, referred to as the chip firing or dollar game.
The group formed by the recurrent configurations, as well as the group <math>\mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta'</math> to which the former is isomorphic, is most commonly referred to as the ''sandpile group''. Other common names for the same group are ''critical group'', ''Jacobian group'' or (less often) ''Picard group''. Note, however, that some authors only denote the group formed by the recurrent configurations as the sandpile group, while reserving the name Jacobian group or critical group for the (isomorphic) group defined by <math>\mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta'</math> (or for related isomorphic definitions). Finally, some authors use the name Picard group to refer to the direct product of the sandpile group and <math>\mathbb{Z}</math>, which naturally appears in a cellular automaton closely related to the sandpile model, referred to as the chip firing or dollar game.
由循环构型形成的群，以及与前者同构的群<math>\mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta'</math>，通常被称为“沙堆群”。同一组的其他常用名称是“关键组”、“雅可比组”或（不太常见的）“Picard组”。然而，请注意，有些作者只将由循环配置形成的组表示为沙堆组，而将Jacobian group或critical group保留为由<math>\mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta'</math>定义的（同构）组的名称。最后，一些作者使用Picard group这个名称来表示sandpile组和<math>\mathbb{Z}</math>的直积，它自然出现在与沙堆模型密切相关的元胞自动机中，被称为芯片点火或美元游戏。
Animation of the sandpile identity on square grids of increasing size. Black color denotes vertices with 0 grains, green is for 1, purple is for 2, and gold is for 3.
Animation of the sandpile identity on square grids of increasing size. Black color denotes vertices with 0 grains, green is for 1, purple is for 2, and gold is for 3.
Given the isomorphisms stated above, the order of the sandpile group is the determinant of <math>\Delta'</math>, which by the [[Kirchhoff's theorem|matrix tree theorem]] is the number of spanning trees of the graph.
Given the isomorphisms stated above, the order of the sandpile group is the determinant of <math>\Delta'</math>, which by the [[Kirchhoff's theorem|matrix tree theorem]] is the number of spanning trees of the graph.
给定上述同构，沙堆群的阶是<math>\Delta'</math>的行列式，根据[[基尔霍夫定理|矩阵树定理]]是图的生成树的数目。
The animation shows the recurrent configuration corresponding to the identity of the sandpile group on different N\times N square grids of increasing sizes N\geq 1, whereby the configurations are rescaled to always have the same physical dimension. Visually, the identities on larger grids seem to become more and more detailed and to "converge to a continuous image". Mathematically, this suggests the existence of scaling-limits of the sandpile identity on square grids based on the notion of weak-* convergence (or some other, generalized notion of convergence). Indeed, existence of scaling limits of recurrent sandpile configurations has been proved by Wesley Pegden and Charles Smart
The animation shows the recurrent configuration corresponding to the identity of the sandpile group on different N\times N square grids of increasing sizes N\geq 1, whereby the configurations are rescaled to always have the same physical dimension. Visually, the identities on larger grids seem to become more and more detailed and to "converge to a continuous image". Mathematically, this suggests the existence of scaling-limits of the sandpile identity on square grids based on the notion of weak-* convergence (or some other, generalized notion of convergence). Indeed, existence of scaling limits of recurrent sandpile configurations has been proved by Wesley Pegden and Charles Smart
==Self-organized criticality==
==Self-organized criticality自组织临界性==
. In further joint work with Lionel Levine, they use the scaling limit to explain the fractal structure of the sandpile on square grids.
. In further joint work with Lionel Levine, they use the scaling limit to explain the fractal structure of the sandpile on square grids.
The original interest behind the model stemmed from the fact that in simulations on lattices, it is attracted to its [[critical state]], at which point the correlation length of the system and the correlation time of the system go to infinity, without any fine tuning of a system parameter. This contrasts with earlier examples of critical phenomena, such as the [[phase transition]]s between solid and liquid, or liquid and gas, where the critical point can only be reached by precise tuning (e.g., of temperature). Hence, in the sandpile model we can say that the criticality is [[self-organization|self-organized]].
The original interest behind the model stemmed from the fact that in simulations on lattices, it is attracted to its [[critical state]], at which point the correlation length of the system and the correlation time of the system go to infinity, without any fine tuning of a system parameter. This contrasts with earlier examples of critical phenomena, such as the [[phase transition]]s between solid and liquid, or liquid and gas, where the critical point can only be reached by precise tuning (e.g., of temperature). Hence, in the sandpile model we can say that the criticality is [[self-organization|self-organized]].
模型背后最初的兴趣源于这样一个事实，即在格子上的模拟中，它被吸引到了它的[[临界状态]]，此时系统的关联长度和系统的关联时间趋于无穷大，而不需要对系统参数进行任何微调。这与早期临界现象的例子形成了对比，例如固体和液体之间，或液体和气体之间的[[相变]]，其中临界点只能通过精确调节（例如，温度）来达到。因此，在沙堆模型中，我们可以说临界性是[[self-organization | self-organization]]。
Once the sandpile model reaches its critical state there is no correlation between the system's response to a [[wiktionary:perturbation|perturbation]] and the details of a perturbation. Generally this means that dropping another grain of sand onto the pile may cause nothing to happen, or it may cause the entire pile to collapse in a massive slide. The model also displays [[1/f noise|1/''ƒ'' noise]], a feature common to many complex systems in nature.
一旦沙堆模型达到其临界状态，系统对[[w]的响应之间没有关联iktionary:扰动|扰动]]和扰动的细节。一般来说，这意味着再往桩上撒一粒沙子可能不会导致任何事情发生，或者可能导致整个桩体在大规模滑坡中倒塌。该模型还显示了[[1/f noise | 1/'&fnof；''noise]]，这是自然界中许多复杂系统的共同特征。
30 million grains dropped to a site of the infinite square grid, then toppled according to the rules of the sandpile model. White color denotes sites with 0 grains, green is for 1, purple is for 2, gold is for 3. The bounding box is 3967×3967.
30 million grains dropped to a site of the infinite square grid, then toppled according to the rules of the sandpile model. White color denotes sites with 0 grains, green is for 1, purple is for 2, gold is for 3. The bounding box is 3967×3967.
This model only displays critical behaviour in two or more dimensions. The sandpile model can be expressed in 1D; however, instead of evolving to its critical state, the 1D sandpile model instead reaches a minimally stable state where every lattice site goes toward the critical slope.
This model only displays critical behaviour in two or more dimensions. The sandpile model can be expressed in 1D; however, instead of evolving to its critical state, the 1D sandpile model instead reaches a minimally stable state where every lattice site goes toward the critical slope.
这个模型只显示两个或更多维度的临界行为。沙堆模型可以用一维来表示，但是，一维沙堆模型并没有进化到临界状态，而是达到了一个最小稳定状态，每个晶格位置都朝着临界坡度方向发展。
A rather popular model on the (infinite) square lattice with sites (x,y)\in\mathbb{Z}^2 is defined as follows:
A rather popular model on the (infinite) square lattice with sites (x,y)\in\mathbb{Z}^2 is defined as follows:
For two dimensions, the associated conformal field theory is suggested to be symplectic fermions with central charge ''c'' = −2.<ref>{{cite journal |author=S. Moghimi-Araghi |author2=M. A. Rajabpour |author3=S. Rouhani |title=Abelian Sandpile Model: a Conformal Field Theory Point of View |arxiv=cond-mat/0410434 |year=2004 |doi=10.1016/j.nuclphysb.2005.04.002 |volume=718|issue=3|journal=Nuclear Physics B|pages=362–370|bibcode = 2005NuPhB.718..362M }}</ref>
For two dimensions, the associated conformal field theory is suggested to be symplectic fermions with central charge ''c'' = −2.<ref>{{cite journal |author=S. Moghimi-Araghi |author2=M. A. Rajabpour |author3=S. Rouhani |title=Abelian Sandpile Model: a Conformal Field Theory Point of View |arxiv=cond-mat/0410434 |year=2004 |doi=10.1016/j.nuclphysb.2005.04.002 |volume=718|issue=3|journal=Nuclear Physics B|pages=362–370|bibcode = 2005NuPhB.718..362M }}</ref>
对于二维，相关共形场理论被认为是中心电荷为“c”的辛费米子； = −2。<ref>{{cite journal |author=S. Moghimi-Araghi |author2=M. A. Rajabpour |author3=S. Rouhani |title=Abelian Sandpile Model: a Conformal Field Theory Point of View |arxiv=cond-mat/0410434 |year=2004 |doi=10.1016/j.nuclphysb.2005.04.002 |volume=718|issue=3|journal=Nuclear Physics B|pages=362–370|bibcode = 2005NuPhB.718..362M }}</ref>
Begin with some nonnegative configuration of values z(x,y)\in \mathbf{Z} which is finite, meaning
Begin with some nonnegative configuration of values z(x,y)\in \mathbf{Z} which is finite, meaning
从 mathbf { z }中值 z (x，y)的一些非负配置开始，这意味着
从 mathbf { z }中值 z (x，y)的一些非负配置开始，这意味着
==Properties==
==Properties属性==
\sum_{x,y}z(x,y)<\infty.
\sum_{x,y}z(x,y)<\infty.
(x，y) < infty.
(x，y) < infty.
===Least action principle===
===Least action principle最小作用原理===
The stabilization of chip configurations obeys a form of ''[[principle of least action|least action principle]]'': each vertex topples no more than necessary in the course of the stabilization.<ref name=Fey2010>
The stabilization of chip configurations obeys a form of ''[[principle of least action|least action principle]]'': each vertex topples no more than necessary in the course of the stabilization.<ref name=Fey2010>
芯片结构的稳定遵循一种“[[最小作用原理|最小作用原理]]”的形式：每个顶点在稳定过程中不超过必要的倾倒量。<ref name=Fey2010>
Any site (x,y) with
Any site (x,y) with
This can be formalized as follows. Call a sequence of topples ''legal'' if it only topples unstable vertices, and ''stabilizing'' if it results in a stable configuration. The standard way of stabilizing the sandpile is to find a maximal legal sequence; i.e., by toppling so long as it is possible. Such a sequence is obviously stabilizing, and the Abelian property of the sandpile is that all such sequences are equivalent up to permutation of the toppling order; that is, for any vertex <math>v</math>, the number of times <math>v</math> topples is the same in all legal stabilizing sequences. According to the least action principle, a '''minimal stabilizing''' sequence is also equivalent up to permutation of the toppling order to a legal (and still stabilizing) sequence. In particular, the configuration resulting from a minimal stabilizing sequence is the same as results from a maximal legal sequence.
This can be formalized as follows. Call a sequence of topples ''legal'' if it only topples unstable vertices, and ''stabilizing'' if it results in a stable configuration. The standard way of stabilizing the sandpile is to find a maximal legal sequence; i.e., by toppling so long as it is possible. Such a sequence is obviously stabilizing, and the Abelian property of the sandpile is that all such sequences are equivalent up to permutation of the toppling order; that is, for any vertex <math>v</math>, the number of times <math>v</math> topples is the same in all legal stabilizing sequences. According to the least action principle, a '''minimal stabilizing''' sequence is also equivalent up to permutation of the toppling order to a legal (and still stabilizing) sequence. In particular, the configuration resulting from a minimal stabilizing sequence is the same as results from a maximal legal sequence.
这可以形式化如下。如果一个倒转序列只推翻不稳定的顶点，则称其为“合法”；如果它导致稳定的配置，则称之为“稳定”。稳定沙堆的标准方法是找到一个最大的合法序列，即只要有可能就倾倒。这样的序列是明显稳定的，沙堆的阿贝尔性质是，所有这些序列都等价于倾倒顺序的置换；也就是说，对于任何顶点<math>v</math>，在所有合法的稳定化序列中，<math>v</math>倒下的次数是相同的。根据最小作用原理，“最小稳定”序列也相当于将倾倒顺序排列成合法（且仍在稳定）序列。特别地，由最小稳定序列得到的配置与从最大合法序列得到的配置相同。
The Bak–Tang–Wiesenfeld sandpile was mentioned on the Numb3rs episode "Rampage," as mathematician Charlie Eppes explains to his colleagues a solution to a criminal investigation.
The Bak–Tang–Wiesenfeld sandpile was mentioned on the Numb3rs episode "Rampage," as mathematician Charlie Eppes explains to his colleagues a solution to a criminal investigation.
More formally, if <math>\mathbf{u}</math> is a vector such that <math>\mathbf{u}(v)</math> is the number of times the vertex <math>v</math> topples during the stabilization (via the toppling of unstable vertices) of a chip configuration <math>z</math>, and <math>\mathbf{n}</math> is an integral vector (not necessarily non-negative) such that <math>z-\mathbf{n}\Delta'</math> is stable, then <math>\mathbf{u}(v) \leq \mathbf{n}(v)</math> for all vertices <math>v</math>.
More formally, if <math>\mathbf{u}</math> is a vector such that <math>\mathbf{u}(v)</math> is the number of times the vertex <math>v</math> topples during the stabilization (via the toppling of unstable vertices) of a chip configuration <math>z</math>, and <math>\mathbf{n}</math> is an integral vector (not necessarily non-negative) such that <math>z-\mathbf{n}\Delta'</math> is stable, then <math>\mathbf{u}(v) \leq \mathbf{n}(v)</math> for all vertices <math>v</math>.
更正式地说，如果<math>\mathbf{u}</math>是一个向量，使得<math>\mathbf{u}（v）</math>是在芯片配置<math>z的稳定过程中（通过不稳定顶点的倒转）顶点<math>v</math>翻转的次数，并且<math>\mathbf{n}</math>是一个积分向量（不一定是非负的），使得<math>z-\mathbf{n}\Delta'</math>是稳定的，那么对于所有顶点<math>v</math>。
The computer game Hexplode is based around the Abelian sandpile model on a finite hexagonal grid where instead of random grain placement, grains are placed by players.
The computer game Hexplode is based around the Abelian sandpile model on a finite hexagonal grid where instead of random grain placement, grains are placed by players.
计算机游戏 Hexplode 是基于有限六边形网格上的阿贝尔沙堆模型，在这个模型中，颗粒由玩家放置，而不是随机的颗粒放置。
计算机游戏 Hexplode 是基于有限六边形网格上的阿贝尔沙堆模型，在这个模型中，颗粒由玩家放置，而不是随机的颗粒放置。
=== Scaling limits ===
=== Scaling limits 缩放限制===
[[File:Scaling sandpile identity.gif|thumb|Animation of the sandpile identity on square grids of increasing size. Black color denotes vertices with 0 grains, green is for 1, purple is for 2, and gold is for 3.]]
[[File:Scaling sandpile identity.gif|thumb|Animation of the sandpile identity on square grids of increasing size. Black color denotes vertices with 0 grains, green is for 1, purple is for 2, and gold is for 3.]]
[[文件：缩放沙堆标识.gif|拇指|动画沙堆身份在正方形网格上不断扩大。黑色表示0颗粒的顶点，绿色表示1，紫色表示2，金色表示3。]]
The animation shows the recurrent configuration corresponding to the identity of the sandpile group on different <math>N\times N</math> square grids of increasing sizes <math>N\geq 1</math>, whereby the configurations are rescaled to always have the same physical dimension. Visually, the identities on larger grids seem to become more and more detailed and to "converge to a continuous image". Mathematically, this suggests the existence of scaling-limits of the sandpile identity on square grids based on the notion of weak-* convergence (or some other, generalized notion of convergence). Indeed, existence of scaling limits of recurrent sandpile configurations has been proved by Wesley Pegden and Charles Smart
The animation shows the recurrent configuration corresponding to the identity of the sandpile group on different <math>N\times N</math> square grids of increasing sizes <math>N\geq 1</math>, whereby the configurations are rescaled to always have the same physical dimension. Visually, the identities on larger grids seem to become more and more detailed and to "converge to a continuous image". Mathematically, this suggests the existence of scaling-limits of the sandpile identity on square grids based on the notion of weak-* convergence (or some other, generalized notion of convergence). Indeed, existence of scaling limits of recurrent sandpile configurations has been proved by Wesley Pegden and Charles Smart
动画显示了与不同的<math>N\times N</math>大小不断增大的<math>N\geq 1</math>正方形网格上的沙堆组标识相对应的重复配置，从而重新缩放配置以始终具有相同的物理维度。从视觉上看，更大网格上的身份似乎变得越来越详细，并且“收敛到一个连续的图像”。从数学上讲，这表明基于弱收敛的概念（或其他一些广义的收敛概念），正方形网格上沙堆恒等式存在标度极限。事实上，Wesley-Pegden和Charles-Smart已经证明了循环沙堆结构标度极限的存在性
<ref name=Pegden2016>{{cite arxiv |last1=Pegden |first1=Wesley |last2=Smart |first2=Charles |title=Stability of patterns in the Abelian sandpile.|eprint=1708.09432 | date=2017 | ref=Pegden2017|class=math.AP }}</ref>
<ref name=Pegden2016>{{cite arxiv |last1=Pegden |first1=Wesley |last2=Smart |first2=Charles |title=Stability of patterns in the Abelian sandpile.|eprint=1708.09432 | date=2017 | ref=Pegden2017|class=math.AP }}</ref>
== Generalizations and related models==
== Generalizations and related models归纳与相关模型==
| author = Per Bak
| author = Per Bak
作者: Per Bak
作者: Per Bak
=== Sandpile models on infinite grids ===
=== Sandpile models on infinite grids 无限网格上的沙堆模型===
| year = 1996
| year = 1996
[[File:Sandpile on infinite grid, 3e7 grains.png|thumb|right|upright=1.25|30 million grains dropped to a site of the infinite square grid, then toppled according to the rules of the sandpile model. White color denotes sites with 0 grains, green is for 1, purple is for 2, gold is for 3. The bounding box is 3967×3967.]]
[[File:Sandpile on infinite grid, 3e7 grains.png|thumb|right|upright=1.25|30 million grains dropped to a site of the infinite square grid, then toppled according to the rules of the sandpile model. White color denotes sites with 0 grains, green is for 1, purple is for 2, gold is for 3. The bounding box is 3967×3967.]]
[[文件：沙堆无限网格，3e7谷物.png|拇指|右|直立=1.25 | 3000万颗谷物落在无限方格网中，然后根据沙堆模型的规则倾倒。白色表示0粒位，绿色代表1，紫色代表2，金色代表3。边框为3967×3967。]]
| title = How Nature Works: The Science of Self-Organized Criticality
| title = How Nature Works: The Science of Self-Organized Criticality
There exist several generalizations of the sandpile model to infinite grids. A challenge in such generalizations is that, in general, it is not guaranteed anymore that every avalanche will eventually stop. Several of the generalization thus only consider the stabilization of configurations for which this can be guaranteed.
There exist several generalizations of the sandpile model to infinite grids. A challenge in such generalizations is that, in general, it is not guaranteed anymore that every avalanche will eventually stop. Several of the generalization thus only consider the stabilization of configurations for which this can be guaranteed.
沙堆模型可以推广到无限网格。这种归纳法的一个挑战是，一般来说，不再保证每次雪崩最终都会停止。因此，一些一般化方法只考虑了能保证这一点的构型的稳定性。
| publisher = Copernicus
| publisher = Copernicus
A rather popular model on the (infinite) square lattice with sites <math>(x,y)\in\mathbb{Z}^2</math> is defined as follows:
A rather popular model on the (infinite) square lattice with sites <math>(x,y)\in\mathbb{Z}^2</math> is defined as follows:
在（无限）方格上有一个相当流行的模型，其位置<math>（x，y）\in\mathbb{Z}^2</math>定义如下：
| isbn = 978-0-387-94791-4
| isbn = 978-0-387-94791-4
Begin with some nonnegative configuration of values <math>z(x,y)\in \mathbf{Z}</math> which is finite, meaning
Begin with some nonnegative configuration of values <math>z(x,y)\in \mathbf{Z}</math> which is finite, meaning
从\mathbf{z}</math>中的值<math>z(x,y)\in \mathbf{Z}</math>的一些非负配置开始，这意味着
:<math>\sum_{x,y}z(x,y)<\infty.</math>
:<math>\sum_{x,y}z(x,y)<\infty.</math>
38
38
=== Sandpile models on directed graphs ===
=== Sandpile models on directed graphs 有向图上的沙堆模型===
| issue = 1
| issue = 1
The sandpile model can be generalized to arbitrary directed multigraphs. The rules are that any vertex <math>v</math> with
The sandpile model can be generalized to arbitrary directed multigraphs. The rules are that any vertex <math>v</math> with
沙堆模型可以推广到任意有向多图。规则是任何顶点<math>v</math>与
| pages = 364–374
| pages = 364–374
is unstable; toppling again sends chips to each of its neighbors, one along each outgoing edge:
is unstable; toppling again sends chips to each of its neighbors, one along each outgoing edge:
为不稳定；再次倾倒会将碎片发送给每个邻居，沿每个出线边缘各一个：
|pmid=9900174 | bibcode=1988PhRvA..38..364B
|pmid=9900174 | bibcode=1988PhRvA..38..364B
and, for each <math>u\neq v</math>:
and, for each <math>u\neq v</math>:
并且，对每个<math>u\neq v</math>:
:<math>z(u) \rightarrow z(u) + \deg(v,u)</math>
:<math>z(u) \rightarrow z(u) + \deg(v,u)</math>
where <math>\deg(v,u)</math> is the number of edges from <math>v</math> to <math>u</math>.
where <math>\deg(v,u)</math> is the number of edges from <math>v</math> to <math>u</math>.
其中<math>\deg（v，u）</math>是从<math>v</math>到<math>u</math>的边数。
| location=Providence, RI | publisher=American Mathematical Society | isbn=978-1-4704-1021-6 | year=2013 | citeseerx=10.1.1.760.283 }}
| location=Providence, RI | publisher=American Mathematical Society | isbn=978-1-4704-1021-6 | year=2013 | citeseerx=10.1.1.760.283 }}
In this case the Laplacian matrix is not symmetric. If we specify a sink <math>s</math> such that there is a path from every other vertex to <math>s</math>, then the stabilization operation on finite graphs is well-defined and the sandpile group can be written
In this case the Laplacian matrix is not symmetric. If we specify a sink <math>s</math> such that there is a path from every other vertex to <math>s</math>, then the stabilization operation on finite graphs is well-defined and the sandpile group can be written
在这种情况下，拉普拉斯矩阵是不对称的。如果我们指定一个sink<math>s</math>，使得每一个顶点都有一条到<math>s</math>的路径，那么有限图上的稳定操作是定义良好的，并且沙堆群可以被写出来
:<math>\mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta'</math>
:<math>\mathbf{Z}^{n-1}/\mathbf{Z}^{n-1}\Delta'</math>
as before.
as before.
如上。
The order of the sandpile group is again the determinant of <math>\Delta'</math>, which by the general version of the [[Kirchhoff's theorem|matrix tree theorem]] is the number of oriented [[spanning tree]]s rooted at the sink.
沙堆群的顺序又是<math>\Delta'</math>的行列式，根据[[Kirchhoff定理|矩阵树定理]]的一般版本，它是这一汇顶点处有向的[[生成树]]的根数。
Category:Self-organization
Category:Self-organization
类别: 阶段转变
类别: 阶段转变
=== The extended sandpile model ===
=== The extended sandpile model 扩展沙堆模型===
Category:Dynamical systems
Category:Dynamical systems
To better understand the structure of the sandpile group for different finite convex grids <math>\Gamma\subset\mathbb{Z}^2</math> of the standard square lattice <math>\mathbb{Z}^2</math>, Lang and Shkolnikov introduced the ''extended sandpile model'' in 2019.<ref name=Lang2019>{{Cite journal|last=Lang|first=Moritz|last2=Shkolnikov|first2=Mikhail|date=2019-02-19|title=Harmonic dynamics of the abelian sandpile|journal=Proceedings of the National Academy of Sciences|language=en|volume=116|issue=8|pages=2821–2830|doi=10.1073/pnas.1812015116|pmid=30728300|pmc=6386721|issn=0027-8424}}</ref> The extended sandpile model is defined nearly exactly the same as the ''usual sandpile model'' (i.e. the original Bak–Tang–Wiesenfeld model <ref name="Bak1987" />), except that vertices at the boundary <math>\partial\Gamma</math> of the grid are now allowed to carry a non-negative real number of grains. In contrast, vertices in the interior of the grid are still only allowed to carry integer numbers of grains. The toppling rules remain unchanged, i.e. both interior and boundary vertices are assumed to become unstable and topple if the grain number reaches or exceeds four.
To better understand the structure of the sandpile group for different finite convex grids <math>\Gamma\subset\mathbb{Z}^2</math> of the standard square lattice <math>\mathbb{Z}^2</math>, Lang and Shkolnikov introduced the ''extended sandpile model'' in 2019.<ref name=Lang2019>{{Cite journal|last=Lang|first=Moritz|last2=Shkolnikov|first2=Mikhail|date=2019-02-19|title=Harmonic dynamics of the abelian sandpile|journal=Proceedings of the National Academy of Sciences|language=en|volume=116|issue=8|pages=2821–2830|doi=10.1073/pnas.1812015116|pmid=30728300|pmc=6386721|issn=0027-8424}}</ref> The extended sandpile model is defined nearly exactly the same as the ''usual sandpile model'' (i.e. the original Bak–Tang–Wiesenfeld model <ref name="Bak1987" />), except that vertices at the boundary <math>\partial\Gamma</math> of the grid are now allowed to carry a non-negative real number of grains. In contrast, vertices in the interior of the grid are still only allowed to carry integer numbers of grains. The toppling rules remain unchanged, i.e. both interior and boundary vertices are assumed to become unstable and topple if the grain number reaches or exceeds four.
为了更好地理解不同有限凸网格的沙堆群的结构，Lang和Shkolnikov在2019年推出了“扩展沙堆模型”。<ref name=Lang2019>{Cite journal | last=Lang | first=Moritz | last2=Shkolnikov | first2=Mikhail | date=2019-02-19 | title=阿贝尔沙堆的谐波动力学| journal=National Academy of the National AcademySciences | language=en | volume=116 | issue=8 | pages=2821–2830 | doi=10.1073/pnas.1812015116 | pmid=30728300 | pmi=6386721 | issn=0027-8424}</ref>扩展沙堆模型的定义与“通常的沙堆模型”几乎完全相同（即原始的Bak–Tang–Wiesenfeld模型<ref name=“Bak1987”/>），除了网格边界<math>\partial\Gamma</math>的顶点现在允许携带非负实数的晶粒。相反，网格内部的顶点仍然只允许携带整数个粒子。倾倒规则保持不变，即假定内部和边界顶点都变得不稳定，并且当晶粒数达到或超过4时会发生倾倒。
Category:Nonlinear systems
Category:Nonlinear systems