仿真鸟群-Python实现（Win11）

参考书籍《Python极客项目编程》。

运行环境

操作系统Win11。

Python 3.10.5。

电脑连接互联网。

安装相关包

在命令行窗口使用pip命令（我的电脑上，“pip.exe”文件所在目录是“D:\Programs\Python\Python310\Scripts”）安装numpy、matplotlib、scipy等相关包，命令如下：

pip install numpy

pip install matplotlib

pip install scipy

并根据提示使用如下命令升级：

D:\Programs\Python\Python310\python.exe -m pip install --upgrade pip

安装包相关信息的查看（以numpy为例）

启动python，进入python提示符，依次键入import numpy、print(numpy)、dir(numpy)；或者help()、numpy，显示该模块的相关信息。（help(numpy)也可以）。

 

源代码

源代码网址： pp/boids.py at master · electronut/pp · GitHub 

源代码如下：

"""
boids.py
Implementation of Craig Reynold's BOIDs
Author: Mahesh Venkitachalam
"""
 
 
 
import sys, argparse
 
import math
 
import numpy as np
 
import matplotlib.pyplot as plt
 
import matplotlib.animation as animation
 
from scipy.spatial.distance import squareform, pdist, cdist
 
from numpy.linalg import norm
 
 
 
width, height = 640, 480
 
 
 
class Boids:
 
    """Class that represents Boids simulation"""
 
    def __init__(self, N):
 
        """ initialize the Boid simulation"""
 
        # init position & velocities
 
        self.pos = [width/2.0, height/2.0] + 10*np.random.rand(2*N).reshape(N, 2)
 
        # normalized random velocities
 
        angles = 2*math.pi*np.random.rand(N)
 
        self.vel = np.array(list(zip(np.sin(angles), np.cos(angles))))
 
        self.N = N
 
        # min dist of approach
 
        self.minDist = 25.0
 
        # max magnitude of velocities calculated by "rules"
 
        self.maxRuleVel = 0.03
 
        # max maginitude of final velocity
 
        self.maxVel = 2.0
 
 
 
    def tick(self, frameNum, pts, beak):
 
        """Update the simulation by one time step."""
 
        # get pairwise distances
 
        self.distMatrix = squareform(pdist(self.pos))
 
        # apply rules:
 
        self.vel += self.applyRules()
 
        self.limit(self.vel, self.maxVel)
 
        self.pos += self.vel
 
        self.applyBC()
 
        # update data
 
        pts.set_data(self.pos.reshape(2*self.N)[::2],
 
                     self.pos.reshape(2*self.N)[1::2])
 
        vec = self.pos + 10*self.vel/self.maxVel
 
        beak.set_data(vec.reshape(2*self.N)[::2],
 
                      vec.reshape(2*self.N)[1::2])
 
 
 
    def limitVec(self, vec, maxVal):
 
        """limit magnitide of 2D vector"""
 
        mag = norm(vec)
 
        if mag > maxVal:
 
            vec[0], vec[1] = vec[0]*maxVal/mag, vec[1]*maxVal/mag
 
    
 
    def limit(self, X, maxVal):
 
        """limit magnitide of 2D vectors in array X to maxValue"""
 
        for vec in X:
 
            self.limitVec(vec, maxVal)
 
            
 
    def applyBC(self):
 
        """apply boundary conditions"""
 
        deltaR = 2.0
 
        for coord in self.pos:
 
            if coord[0] > width + deltaR:
 
                coord[0] = - deltaR
 
            if coord[0] < - deltaR:
 
                coord[0] = width + deltaR    
 
            if coord[1] > height + deltaR:
 
                coord[1] = - deltaR
 
            if coord[1] < - deltaR:
 
                coord[1] = height + deltaR
 
    
 
    def applyRules(self):
 
        # apply rule #1 - Separation
 
        D = self.distMatrix < 25.0
 
        vel = self.pos*D.sum(axis=1).reshape(self.N, 1) - D.dot(self.pos)
 
        self.limit(vel, self.maxRuleVel)
 
 
 
        # different distance threshold
 
        D = self.distMatrix < 50.0
 
 
 
        # apply rule #2 - Alignment
 
        vel2 = D.dot(self.vel)
 
        self.limit(vel2, self.maxRuleVel)
 
        vel += vel2;
 
 
 
        # apply rule #1 - Cohesion
 
        vel3 = D.dot(self.pos) - self.pos
 
        self.limit(vel3, self.maxRuleVel)
 
        vel += vel3
 
 
 
        return vel
 
 
 
    def buttonPress(self, event):
 
        """event handler for matplotlib button presses"""
 
        # left click - add a boid
 
        if event.button is 1:
 
            self.pos = np.concatenate((self.pos,
 
                                       np.array([[event.xdata, event.ydata]])),
 
                                      axis=0)
 
            # random velocity
 
            angles = 2*math.pi*np.random.rand(1)
 
            v = np.array(list(zip(np.sin(angles), np.cos(angles))))
 
            self.vel = np.concatenate((self.vel, v), axis=0)
 
            self.N += 1
 
        # right click - scatter
 
        elif event.button is 3:
 
            # add scattering velocity
 
            self.vel += 0.1*(self.pos - np.array([[event.xdata, event.ydata]]))
 
        
 
def tick(frameNum, pts, beak, boids):
 
    #print frameNum
 
    """update function for animation"""
 
    boids.tick(frameNum, pts, beak)
 
    return pts, beak
 
 
 
# main() function
 
def main():
 
  # use sys.argv if needed
 
  print('starting boids...')
 
 
 
  parser = argparse.ArgumentParser(description="Implementing Craig Reynold's Boids...")
 
  # add arguments
 
  parser.add_argument('--num-boids', dest='N', required=False)
 
  args = parser.parse_args()
 
 
 
  # number of boids
 
  N = 100
 
  if args.N:
 
      N = int(args.N)
 
 
 
  # create boids
 
  boids = Boids(N)
 
 
 
  # setup plot
 
  fig = plt.figure()
 
  ax = plt.axes(xlim=(0, width), ylim=(0, height))
 
 
 
  pts, = ax.plot([], [], markersize=10,
 
                  c='k', marker='o', ls='None')
 
  beak, = ax.plot([], [], markersize=4,
 
                  c='r', marker='o', ls='None')
 
  anim = animation.FuncAnimation(fig, tick, fargs=(pts, beak, boids),
 
                                 interval=50)
 
 
 
  # add a "button press" event handler
 
  cid = fig.canvas.mpl_connect('button_press_event', boids.buttonPress)
 
 
 
  plt.show()
 
 
 
# call main
 
if __name__ == '__main__':
 
  main()

运行结果

将上述代码保存为文件“d:\temp\boids.py”。

在命令行窗口执行命令 “python d:\temp\boids.py”，运行结果如下：