浮动不正确？ -Python 2.6

发布于 2024-09-17 05:11:41 字数 6696 浏览 1 评论 0原文

我有一个编程问题，如下所示，我的解决方案无法产生所需的输出

这个粒子模拟器在一个与我们的物理定律不同的宇宙中运行。每个粒子都有一个位置 (x, y)、速度 (vx, vy) 和加速度 (ax, ay)。每个粒子都对其他粒子施加吸引力。无论粒子距离多远，这个力都是相同的。
粒子在 x 方向上的加速度由下式给出：
(ax=x右侧的粒子数−x左侧的粒子数)/10.0
粒子将以速度 vx + ax 向左或向右移动。
类似地，粒子在 y 方向上的加速度由下式给出：
(ay=y上方的粒子数−y下方的粒子数)/10.0
粒子将以速度 vy + ay 向上或向下移动。
颗粒被束缚在尺寸为-300＜1的室中。 x < 300和-200＜ y < 200. 如果一个粒子撞击到室壁，它应该反弹。弹跳涉及将 x 或 y 坐标设置为边界，并反转速度方向。例如，如果粒子最终位置为 x=305，则应设置 x=300 且 vx = -vx。请注意，x 必须设置为整数值 300，才能获得与测试用例相同的输出值。
编写一个程序来读取名为 keywords.txt 的文件，其中包含多个粒子的初始位置、速度和加速度。文件的第一行包含运行模拟的迭代次数（本例中为 5）。每隔一行包含有关一个粒子的数据，格式为 xy vx vy ax ay，如下所示：
5
0 -30 3 0 0 0
100 50 0 1 0 0
20 10 0 3 0 0
-80 15 2 -2 0 0
您的程序应该创建一个粒子对象来存储每个粒子的数据。然后对于模拟的每次迭代你应该
计算每个粒子的加速度（使用上面的方程）
然后计算每个粒子的新速度 (vx = vx + ax)
然后计算每个粒子的新位置 (x = x + vx)
程序的输出应该是模拟每个步骤中每个粒子的位置列表，对于上面所示的 4 粒子示例，采用 CSV 格式 x1,y1,x2,y2,x3,y3,x4,y4 :
3.1,-29.7,99.7,50.7,19.9,13.1,-77.7,12.9
6.3,-29.1,99.1,51.1,19.7,16.1,-75.1,10.9
9.6,-28.2,98.2,51.2,19.4,19.0,-72.2,9.0
13.0,-27.0,97.0,51.0,19.0,21.8,-69.0,7.2
16.5,-25.5,95.5,50.5,18.5,24.5,-65.5,5.5
要生成这些数字，您应该对每个粒子的 x 和 y 坐标调用 str。

我的代码如下：

class Particle(object):
    def __init__(self, (x, y, vx, vy, ax, ay)):
        # Set initial values
        self.x, self.y = float(x), float(y)
        self.vx, self.vy = float(vx), float(vy)
        self.ax, self.ay = float(ax), float(ay)

    def __str__(self):
        return '(' + str(self.x) + ', ' + str(self.y) + ')'

    # Calculate new acceleration
    def calc_acc(self, part_list):
        left, right = 0, 0
        up, down = 0, 0
        for particle in part_list:
            # Count particles on left & right
            if particle.x < self.x:
                left += 1
            elif particle.x > self.x:
                right += 1
            # Count particles above & below
            if particle.y > self.y:
                up += 1
            elif particle.y < self.y:
                down += 1
        # Calculate x-acceleration
        self.ax = (right - left) / 10.0
        # Calculate y-acceleration
        self.ay = (up - down) / 10.0

    # Calculate new velocity
    def calc_vel(self):
        self.vx = self.vx + self.ax
        self.vy = self.vy + self.ay

    # Move the particle
    def move(self, p_list):
        # Calculate new acceleration & velocity
        self.calc_acc(p_list)
        self.calc_vel()
        # Make move
        self.x += self.vx
        self.y += self.vy
        # Check for bounce, and bounce
        # X-axis
        if self.x > 300.0:
            self.x = 300
            self.vx = -(self.vx)
        elif self.x < -300.0:
            self.x = -300
            self.vx = -(self.vx)
        # Y-axis
        if self.y > 200.0:
            self.y = 200
            self.vy = -(self.vy)
        elif self.y < -200.0:
            self.y = -200
            self.vy = -(self.vy)
        # Return resulting position
        return self.x, self.y

# Take file input
input_file = []
for line in open('particles2.txt', 'rU'):
    input_file.append(line)

# Take number of iterations, and leave particle info only
times = int(input_file.pop(0))

# Remove '\n' from particle info, and convert particle info to a list of floats
for line in input_file:
    input_file[input_file.index(line)] = line.strip('\n').split()

# Create list of Particle objects
particles = []
for line in input_file:
    particles.append(Particle(line))

# Create result position array
results = []
for i in range(times):
    results.append([None for x in range(len(particles))])

# Run simulation for 'times' iterations
for iteration in range(times):
    i = 0
    for particle in particles:
        results[iteration][i] = particle.move(particles)
        i += 1

# Create csv formatted string for output
result_output = ''
for iteration in results:
    for particle in iteration:
        result_output += str(particle[0]) + ',' + str(particle[1]) + ','
    result_output += '\n'

result_output = result_output.replace(',\n', '\n')

print result_output

输出是：

21.9,2.0,-18.9,10.1
23.7,4.1,-17.7,20.1
25.4,6.3,-16.4,30.0
27.0,8.6,-15.0,39.8
28.5,11.0,-13.5,49.5
29.9,13.5,-11.9,59.1
31.2,16.1,-10.2,68.6
32.4,18.8,-8.4,78.0
33.5,21.6,-6.5,87.3
34.5,24.5,-4.5,96.5
35.4,27.5,-2.4,105.6
36.2,30.6,-0.2,114.6
36.9,33.8,2.1,123.5
37.5,37.1,4.5,132.3
38.0,40.5,7.0,141.0
38.4,44.0,9.6,149.6
38.7,47.6,12.3,158.1
38.9,51.3,15.1,166.5
39.0,55.1,18.0,174.8
39.0,59.0,21.0,183.0
38.9,63.0,24.1,191.1
38.7,67.1,27.3,199.1
38.4,71.3,30.6,200
38.0,75.6,34.0,192.0
37.5,80.0,37.5,183.9
37.1,84.5,40.9,175.7
36.8,89.1,44.2,167.4
36.6,93.8,47.4,159.0
36.5,98.6,50.5,150.5
36.5,103.5,53.5,141.9
36.6,108.5,56.4,133.2
36.8,113.6,59.2,124.4
37.1,118.8,61.9,115.5
37.5,123.9,64.5,106.7
38.0,128.9,67.0,98.0
38.6,133.8,69.4,89.4
39.3,138.6,71.7,80.9
40.1,143.3,73.9,72.5
41.0,147.9,76.0,64.2
42.0,152.4,78.0,56.0
43.1,156.8,79.9,47.9
44.3,161.1,81.7,39.9
45.6,165.3,83.4,32.0
47.0,169.4,85.0,24.2
48.5,173.4,86.5,16.5
50.1,177.3,87.9,8.9
51.8,181.1,89.2,1.4
53.6,184.8,90.4,-6.0
55.5,188.4,91.5,-13.3
57.5,191.9,92.5,-20.5

当它应该是：

21.9,2.0,-18.9,10.0
23.7,4.1,-17.7,19.9
25.4,6.3,-16.4,29.7
27.0,8.6,-15.0,39.4
28.5,11.0,-13.5,49.0
29.9,13.5,-11.9,58.5
31.2,16.1,-10.2,67.9
32.4,18.8,-8.4,77.2
33.5,21.6,-6.5,86.4
34.5,24.5,-4.5,95.5
35.4,27.5,-2.4,104.5
36.2,30.6,-0.2,113.4
36.9,33.8,2.1,122.2
37.5,37.1,4.5,130.9
38.0,40.5,7.0,139.5
38.4,44.0,9.6,148.0
38.7,47.6,12.3,156.4
38.9,51.3,15.1,164.7
39.0,55.1,18.0,172.9
39.0,59.0,21.0,181.0
38.9,63.0,24.1,189.0
38.7,67.1,27.3,196.9
38.4,71.3,30.6,200
38.0,75.6,34.0,192.1
37.5,80.0,37.5,184.1
37.1,84.5,40.9,176.0
36.8,89.1,44.2,167.8
36.6,93.8,47.4,159.5
36.5,98.6,50.5,151.1
36.5,103.5,53.5,142.6
36.6,108.5,56.4,134.0
36.8,113.6,59.2,125.3
37.1,118.8,61.9,116.5
37.5,123.9,64.5,107.8
38.0,128.9,67.0,99.2
38.6,133.8,69.4,90.7
39.3,138.6,71.7,82.3
40.1,143.3,73.9,74.0
41.0,147.9,76.0,65.8
42.0,152.4,78.0,57.7
43.1,156.8,79.9,49.7
44.3,161.1,81.7,41.8
45.6,165.3,83.4,34.0
47.0,169.4,85.0,26.3
48.5,173.4,86.5,18.7
50.1,177.3,87.9,11.2
51.8,181.1,89.2,3.8
53.6,184.8,90.4,-3.5
55.5,188.4,91.5,-10.7
57.5,191.9,92.5,-17.8

由于某种原因，我无法找到，最后一列中的浮点数不太正确。它们与所需的输出相差 2 到 0.5 左右。

我不知道为什么会这样！

感谢您的帮助！

原文

I have a programming question, as follows, for which my solution does not produce the desired output

This particle simulator operates in a universe with different laws of physics to ours. Each particle has a position (x, y), velocity (vx, vy) and an acceleration (ax, ay). Every particle exerts an attractive force on every other particle. This force is the same regardless of how far away the particle is.
The acceleration of a particle in the x direction is given by
(ax=number of particles to right of x−number of particles to left of x) / 10.0
The particle will then move left or right with velocity vx + ax.
Similarly, the acceleration of a particle in the y direction is given by
(ay=number of particles above y−number of particles below y) / 10.0
The particle will then move up or down with velocity vy + ay.
The particles are bound in a chamber with dimensions −300 < x < 300 and −200 < y < 200. If a particle hits the wall of the chamber it should bounce. Bouncing involves setting the x or y coordinate to the boundary, and reversing the direction of the velocity. For example, if a particle ends up with position x=305 then you should set x=300 and vx = -vx. Note that x must be set to the integer value 300 in order to get the same output values as our test cases.
Write a program to read in a file named particles.txt containing the initial positions, velocities and accelerations of a number of particles. The first line of the file contains the number of iterations to run the simulation for (5 in this example). Every other row contains data about one particle, in the format x y vx vy ax ay like this:
5
0 -30 3 0 0 0
100 50 0 1 0 0
20 10 0 3 0 0
-80 15 2 -2 0 0
Your program should create a Particle object to store the data for each particle. Then for every iteration of the simulation you should
calculate the acceleration on each particle (using the equations above)
then calculate the new velocity for each particle (vx = vx + ax)
then calculate the new position for each particle (x = x + vx)
The output of your program should be a list of positions for each particle at every step of the simulation, in CSV format x1,y1,x2,y2,x3,y3,x4,y4 for the 4-particle example shown above:
3.1,-29.7,99.7,50.7,19.9,13.1,-77.7,12.9
6.3,-29.1,99.1,51.1,19.7,16.1,-75.1,10.9
9.6,-28.2,98.2,51.2,19.4,19.0,-72.2,9.0
13.0,-27.0,97.0,51.0,19.0,21.8,-69.0,7.2
16.5,-25.5,95.5,50.5,18.5,24.5,-65.5,5.5
To produce these numbers, you should call str on the x and y coordinates of each of the particles.

My code is as follows:

class Particle(object):
    def __init__(self, (x, y, vx, vy, ax, ay)):
        # Set initial values
        self.x, self.y = float(x), float(y)
        self.vx, self.vy = float(vx), float(vy)
        self.ax, self.ay = float(ax), float(ay)

    def __str__(self):
        return '(' + str(self.x) + ', ' + str(self.y) + ')'

    # Calculate new acceleration
    def calc_acc(self, part_list):
        left, right = 0, 0
        up, down = 0, 0
        for particle in part_list:
            # Count particles on left & right
            if particle.x < self.x:
                left += 1
            elif particle.x > self.x:
                right += 1
            # Count particles above & below
            if particle.y > self.y:
                up += 1
            elif particle.y < self.y:
                down += 1
        # Calculate x-acceleration
        self.ax = (right - left) / 10.0
        # Calculate y-acceleration
        self.ay = (up - down) / 10.0

    # Calculate new velocity
    def calc_vel(self):
        self.vx = self.vx + self.ax
        self.vy = self.vy + self.ay

    # Move the particle
    def move(self, p_list):
        # Calculate new acceleration & velocity
        self.calc_acc(p_list)
        self.calc_vel()
        # Make move
        self.x += self.vx
        self.y += self.vy
        # Check for bounce, and bounce
        # X-axis
        if self.x > 300.0:
            self.x = 300
            self.vx = -(self.vx)
        elif self.x < -300.0:
            self.x = -300
            self.vx = -(self.vx)
        # Y-axis
        if self.y > 200.0:
            self.y = 200
            self.vy = -(self.vy)
        elif self.y < -200.0:
            self.y = -200
            self.vy = -(self.vy)
        # Return resulting position
        return self.x, self.y

# Take file input
input_file = []
for line in open('particles2.txt', 'rU'):
    input_file.append(line)

# Take number of iterations, and leave particle info only
times = int(input_file.pop(0))

# Remove '\n' from particle info, and convert particle info to a list of floats
for line in input_file:
    input_file[input_file.index(line)] = line.strip('\n').split()

# Create list of Particle objects
particles = []
for line in input_file:
    particles.append(Particle(line))

# Create result position array
results = []
for i in range(times):
    results.append([None for x in range(len(particles))])

# Run simulation for 'times' iterations
for iteration in range(times):
    i = 0
    for particle in particles:
        results[iteration][i] = particle.move(particles)
        i += 1

# Create csv formatted string for output
result_output = ''
for iteration in results:
    for particle in iteration:
        result_output += str(particle[0]) + ',' + str(particle[1]) + ','
    result_output += '\n'

result_output = result_output.replace(',\n', '\n')

print result_output

output is:

21.9,2.0,-18.9,10.1
23.7,4.1,-17.7,20.1
25.4,6.3,-16.4,30.0
27.0,8.6,-15.0,39.8
28.5,11.0,-13.5,49.5
29.9,13.5,-11.9,59.1
31.2,16.1,-10.2,68.6
32.4,18.8,-8.4,78.0
33.5,21.6,-6.5,87.3
34.5,24.5,-4.5,96.5
35.4,27.5,-2.4,105.6
36.2,30.6,-0.2,114.6
36.9,33.8,2.1,123.5
37.5,37.1,4.5,132.3
38.0,40.5,7.0,141.0
38.4,44.0,9.6,149.6
38.7,47.6,12.3,158.1
38.9,51.3,15.1,166.5
39.0,55.1,18.0,174.8
39.0,59.0,21.0,183.0
38.9,63.0,24.1,191.1
38.7,67.1,27.3,199.1
38.4,71.3,30.6,200
38.0,75.6,34.0,192.0
37.5,80.0,37.5,183.9
37.1,84.5,40.9,175.7
36.8,89.1,44.2,167.4
36.6,93.8,47.4,159.0
36.5,98.6,50.5,150.5
36.5,103.5,53.5,141.9
36.6,108.5,56.4,133.2
36.8,113.6,59.2,124.4
37.1,118.8,61.9,115.5
37.5,123.9,64.5,106.7
38.0,128.9,67.0,98.0
38.6,133.8,69.4,89.4
39.3,138.6,71.7,80.9
40.1,143.3,73.9,72.5
41.0,147.9,76.0,64.2
42.0,152.4,78.0,56.0
43.1,156.8,79.9,47.9
44.3,161.1,81.7,39.9
45.6,165.3,83.4,32.0
47.0,169.4,85.0,24.2
48.5,173.4,86.5,16.5
50.1,177.3,87.9,8.9
51.8,181.1,89.2,1.4
53.6,184.8,90.4,-6.0
55.5,188.4,91.5,-13.3
57.5,191.9,92.5,-20.5

when it should be:

21.9,2.0,-18.9,10.0
23.7,4.1,-17.7,19.9
25.4,6.3,-16.4,29.7
27.0,8.6,-15.0,39.4
28.5,11.0,-13.5,49.0
29.9,13.5,-11.9,58.5
31.2,16.1,-10.2,67.9
32.4,18.8,-8.4,77.2
33.5,21.6,-6.5,86.4
34.5,24.5,-4.5,95.5
35.4,27.5,-2.4,104.5
36.2,30.6,-0.2,113.4
36.9,33.8,2.1,122.2
37.5,37.1,4.5,130.9
38.0,40.5,7.0,139.5
38.4,44.0,9.6,148.0
38.7,47.6,12.3,156.4
38.9,51.3,15.1,164.7
39.0,55.1,18.0,172.9
39.0,59.0,21.0,181.0
38.9,63.0,24.1,189.0
38.7,67.1,27.3,196.9
38.4,71.3,30.6,200
38.0,75.6,34.0,192.1
37.5,80.0,37.5,184.1
37.1,84.5,40.9,176.0
36.8,89.1,44.2,167.8
36.6,93.8,47.4,159.5
36.5,98.6,50.5,151.1
36.5,103.5,53.5,142.6
36.6,108.5,56.4,134.0
36.8,113.6,59.2,125.3
37.1,118.8,61.9,116.5
37.5,123.9,64.5,107.8
38.0,128.9,67.0,99.2
38.6,133.8,69.4,90.7
39.3,138.6,71.7,82.3
40.1,143.3,73.9,74.0
41.0,147.9,76.0,65.8
42.0,152.4,78.0,57.7
43.1,156.8,79.9,49.7
44.3,161.1,81.7,41.8
45.6,165.3,83.4,34.0
47.0,169.4,85.0,26.3
48.5,173.4,86.5,18.7
50.1,177.3,87.9,11.2
51.8,181.1,89.2,3.8
53.6,184.8,90.4,-3.5
55.5,188.4,91.5,-10.7
57.5,191.9,92.5,-17.8

For some reason, which I am unable to locate, the floats in the last column are not quite right. They differ from the desired output by anything between 2 and 0.5 or so.

I have no idea why this is the case!

Thanks for any help!

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末が日狂欢 2024-09-24 05:11:41

您需要制作状态快照并在快照上执行计算。如果您在计算过程中像当前一样移动粒子，您将得到不一致的结果。

像这样的东西可能会起作用

from copy import deepcopy
for iteration in range(times):
    i = 0
    particles_snapshot = deepcopy(particles)
    for particle in particles:
        results[iteration][i] = particle.move(particles_snapshot)
        i += 1

You need to make a snapshot of the state and perform your calculations on the snapshot. If you move the particles around during the calculations as you are currently doing, you will get inconsistent results.

Something like this may work

from copy import deepcopy
for iteration in range(times):
    i = 0
    particles_snapshot = deepcopy(particles)
    for particle in particles:
        results[iteration][i] = particle.move(particles_snapshot)
        i += 1

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