Repast Simphony僵尸模型入门教程

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"RepastS使用指南" RepastS是一个开源的多尺度建模平台，主要用于创建和模拟复杂系统，尤其在社会科学、生物学和计算机科学等领域广泛应用。本资源是一份官方入门教程，通过一个僵尸与人类互动的模型来引导用户熟悉RepastS的基本操作。在开始使用RepastS之前，确保已经正确安装了RepastSimphony 2.0版本至关重要。安装指南可在Repast官方网站上找到，涵盖了多种操作系统平台的详细步骤。完成安装后，便可以启动RepastSimphony并开始构建模型。 1. 开始使用RepastSimphony for Java 我们将构建一个简单的基于代理的模型，这个模型描绘的是僵尸追逐人类，而人类则试图逃离僵尸的情景。最终运行的模型效果应如图1所示，展示了一个动态的追逐场景。构建模型的第一步是创建一个新的RepastSimphony项目。启动RepastSimphony后，在“Package Explorer”面板中右键点击，选择“新建”然后选择“其他”。接着会弹出一个对话框，从中选取"Repast Simphony Project"（位于“RepastSimphony”文件夹下）。点击“下一步”，将打开“New Repast Simphony Project Wizard”，在这里可以为项目命名（还有其他选项，但初学者可以暂时忽略）。输入项目名称“jzombies”并继续。 2. 创建模型组件在项目创建后，我们需要定义模型的组成部分，包括代理（如僵尸和人类）、空间环境以及交互规则。在RepastSimphony中，代理有自己的行为逻辑，并能够在模型空间内移动和交互。僵尸和人类代理可能包含如追逐、逃跑、随机移动等行为。空间环境通常用网格或连续空间来表示，代理在其中占据特定位置。 3. 编写代码接下来，需要编写Java代码来实现代理的行为和模型逻辑。RepastSimphony提供了一系列的API和工具，如JShell，用于方便地测试和调试代码。例如，可以创建两个类——`Zombie` 和 `Human`，分别代表僵尸和人类，并为它们定义行为方法。同时，还需要定义如何初始化这些代理，以及它们如何在环境中移动和相互作用。 4. 设计模型参数在模型中，可能需要设置一些参数，比如僵尸和人类的数量、他们的移动速度、追逐和逃跑的概率等。这些参数可以通过RepastSimphony的控制台或者配置文件进行设定，以便在运行时调整和分析模型行为的敏感性。 5. 模型运行与可视化完成代码编写后，可以通过RepastSimphony的运行界面启动模型。模型运行时，其状态会被实时显示，可以观察到僵尸和人类的动态行为。RepastSimphony的强大的可视化功能使得模型的运行结果直观易懂。 6. 分析与结果在模型运行过程中，可以收集数据并进行分析。RepastSimphony提供了各种统计和绘图工具，帮助理解模型的行为模式。例如，可以追踪僵尸和人类的数量变化，或者绘制他们在空间中的分布情况。 7. 进一步学习作为入门教程，这个僵尸模型只是RepastSimphony能力的一个简单示例。随着对平台的深入理解和实践，可以创建更复杂的模型，应用到更多领域，如城市规划、生物种群动态、社会经济系统等。总结来说，RepastS是一个强大的建模工具，通过这个僵尸模型，初学者能够快速了解如何在RepastSimphony中创建、运行和分析基于代理的模型。随着对RepastSimphony特性的掌握，用户可以开发出更加精细和复杂的模拟系统，以解决实际问题。

REPAST JAVA GETTING STARTED 7

the contents and location of the 8 neighboring cells around a GridPoint. The constructor

to GridCellNgh takes the grid whose cells we want to get, the point whose neighboring

grid cells we want, the Class of the items we want in the cells, and the extent along the

appropriate dimensions. Lines 7 and 8 specify the grid and the location of this Zombie

as the point whose neighboring cells we want. By specifying the Human class in the

constructor and as a template parameter we ﬁlter out any non-Humans. Consequently, our

GridCells will on contain Humans. We then call getNeighborhood passing true to it. By

passing true the returned list of GridCells will contain the center cell where the Zombie

is currently located. Using SimUtilities.shuffle, we shuﬄe the list of GridCells.

Without the shuﬄe, the Zombies will always move in the same direction when all cells

are equal. We use the RandomHelper class to provide us with a random generator for the

shuﬄe. The remaining code iterates through the list of GridCells and determines which

one of them has the largest size. A GridCell’s size is a measure of the number of objects

it contains and thus the cell with the greatest size contains the most Humans.

Now that we have discovered the location with the most Humans (i.e. pointWithMostHumans),

we want to move the Zombie towards that location. We will ﬁrst write this method then

add the code to call it in the step() method.

1 public void moveTo wards ( GridPoin t pt ) {

2 // only move if we are not already in this grid loca tio n

3 if (! pt . equals ( grid . ge tLocati on ( this ))) {

4 NdPoint myPoint = space . getLo ca tion ( this );

5 NdPoint othe rPoin t = new NdPoint ( pt . getX () , pt . getY ());

6 double angle = Spat ia lMath . ca lcAng le Fo r2DMo ve ment ( space ,

7 myPoint , oth erPoi nt );

8 space . m ov eByVector ( this , 1 , angle , 0);

9 myPoint = space . g et Locatio n ( this );

10 grid . moveTo ( this , ( int ) myPoint . getX () , ( int ) myPoint . getY ());

11 }

12 }

Listing 4. moveTowards Method

moveTowards() begins with a check to make sure that the Zombie is not already at the

location we want to move towards. Then we get the Zombies current location in space

as a NdPoint. NdPoint stores its coordinates as doubles and thus it is appropriate when

working with ContinuousSpaces. We want the Zombie to move towards the GridPoint pt,

but in order to make this sort of movement using a ContinuousSpace we need to convert

that GridPoint to a NdPoint. Line 5 does that. We then use the SpatialMath method

calcAngleFor2DMovement to calculate the angle along which the Zombie should move if

it is to move towards the GridPoint. Line 8 then performs this movement and moves

the Zombie in the ContinuousSpace 1 units along the calculated angle. The last two lines

8 NICK COLLIER & MICHAEL NORTH - REPAST DEVELOPMENT TEAM

update the Zombies position in the Grid by converting its location in the ContinuousSpace

to int coordinates appropriate for a Grid.

Once you’ve written this moveTowards() method, add a call to it in the step() method.

The end of the step() should now look like:

1 for ( GridCell < Human > cell : gridC ells ) {

2 if ( cell . size () > maxCount ) {

3 p oi nt Wi thMostH um an s = cell . getPoint ();

4 maxCo unt = cell . size ();

5 }

6 }

7 mo veTowar ds ( po in tWithMo st Hu mans );

Listing 5. Step with MoveTowards Added

Note the addition of the call to moveTowards() following the for loop.

We want the step method to be called every iteration of the simulation. We can do this

by adding an @ScheduledMethod annotation on it. Obviously, the method itself is part of a

class, and thus what we are actually scheduling are invocations of this method on instances

of this class. For example, if we have 10 Zombies, then we can schedule this method to be

called on each of those Zombies. The annotation has a variety of parameters that are used

to specify when and how often the method will be called, the number of object instances

to invoke the method on, and so on.

1 @ScheduledMethod ( start = 1 , interval = 1)

2 public void step () {

3 // get the grid location of this Zombie

4 GridP oint pt = grid . getLoc at ion ( this );

Listing 6. Step Method with Annotation

The parameters here in line 1 will schedule the step method to be called on all Zombies

starting at tick (timestep) 1 and every tick thereafter.

Let’s now turn to the code for the Humans. Select Human.java in Eclipse’s editor

pane. The basic behavior for a Human is to react when a Zombie comes within its local

neighborhood by running away from the area with the most Zombies. Additionally, Humans

have a certain amount of energy that is expended in running away. If this energy is 0 or

less then a Human is unable to run. We begin by creating the relevant ﬁeld variables and

constructor.

See the Repast Java API documentation and the Repast Reference for more information on the

@ScheduledMethod annotation.

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