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： https://github.com/electronut/pp/blob/master/boids/boids.py

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：