in_degrees = dict((node,0) for node in self.topology)

这段代码是用来创建一个字典 `in_degrees`，其中键是图的节点，值是节点的入度（即指向该节点的边的数量）。`self.topology` 是一个图的节点集合。

这行代码使用了字典推导式来创建字典 `in_degrees`。它遍历 `self.topology` 中的每个节点，并将该节点作为键，对应的初始值设为 0。最后，返回一个包含节点和对应入度的字典。

相关问题

详细解释以下Python代码：import numpy as np import adi import matplotlib.pyplot as plt sample_rate = 1e6 # Hz center_freq = 915e6 # Hz num_samps = 100000 # number of samples per call to rx() sdr = adi.Pluto("ip:192.168.2.1") sdr.sample_rate = int(sample_rate) # Config Tx sdr.tx_rf_bandwidth = int(sample_rate) # filter cutoff, just set it to the same as sample rate sdr.tx_lo = int(center_freq) sdr.tx_hardwaregain_chan0 = -50 # Increase to increase tx power, valid range is -90 to 0 dB # Config Rx sdr.rx_lo = int(center_freq) sdr.rx_rf_bandwidth = int(sample_rate) sdr.rx_buffer_size = num_samps sdr.gain_control_mode_chan0 = 'manual' sdr.rx_hardwaregain_chan0 = 0.0 # dB, increase to increase the receive gain, but be careful not to saturate the ADC # Create transmit waveform (QPSK, 16 samples per symbol) num_symbols = 1000 x_int = np.random.randint(0, 4, num_symbols) # 0 to 3 x_degrees = x_int*360/4.0 + 45 # 45, 135, 225, 315 degrees x_radians = x_degrees*np.pi/180.0 # sin() and cos() takes in radians x_symbols = np.cos(x_radians) + 1j*np.sin(x_radians) # this produces our QPSK complex symbols samples = np.repeat(x_symbols, 16) # 16 samples per symbol (rectangular pulses) samples *= 2**14 # The PlutoSDR expects samples to be between -2^14 and +2^14, not -1 and +1 like some SDRs # Start the transmitter sdr.tx_cyclic_buffer = True # Enable cyclic buffers sdr.tx(samples) # start transmitting # Clear buffer just to be safe for i in range (0, 10): raw_data = sdr.rx() # Receive samples rx_samples = sdr.rx() print(rx_samples) # Stop transmitting sdr.tx_destroy_buffer() # Calculate power spectral density (frequency domain version of signal) psd = np.abs(np.fft.fftshift(np.fft.fft(rx_samples)))**2 psd_dB = 10*np.log10(psd) f = np.linspace(sample_rate/-2, sample_rate/2, len(psd)) # Plot time domain plt.figure(0) plt.plot(np.real(rx_samples[::100])) plt.plot(np.imag(rx_samples[::100])) plt.xlabel("Time") # Plot freq domain plt.figure(1) plt.plot(f/1e6, psd_dB) plt.xlabel("Frequency [MHz]") plt.ylabel("PSD") plt.show()，并分析该代码中QPSK信号的功率谱密度图的特点

这段Python代码的作用是使用ADI Pluto SDR设备生成并传输一个QPSK信号，并将接收到的信号进行功率谱密度分析。下面是对代码的注释：

import numpy as np
import adi
import matplotlib.pyplot as plt

# 设置采样率、中心频率和采样点数
sample_rate = 1e6 # Hz
center_freq = 915e6 # Hz
num_samps = 100000 # number of samples per call to rx()

# 连接ADI Pluto SDR设备
sdr = adi.Pluto("ip:192.168.2.1")
sdr.sample_rate = int(sample_rate)

# 配置发送端的参数
sdr.tx_rf_bandwidth = int(sample_rate) # filter cutoff, just set it to the same as sample rate
sdr.tx_lo = int(center_freq)
sdr.tx_hardwaregain_chan0 = -50 # Increase to increase tx power, valid range is -90 to 0 dB

# 配置接收端的参数
sdr.rx_lo = int(center_freq)
sdr.rx_rf_bandwidth = int(sample_rate)
sdr.rx_buffer_size = num_samps
sdr.gain_control_mode_chan0 = 'manual'
sdr.rx_hardwaregain_chan0 = 0.0 # dB, increase to increase the receive gain, but be careful not to saturate the ADC

# 创建发送的QPSK信号
num_symbols = 1000
x_int = np.random.randint(0, 4, num_symbols) # 0 to 3
x_degrees = x_int*360/4.0 + 45 # 45, 135, 225, 315 degrees
x_radians = x_degrees*np.pi/180.0 # sin() and cos() takes in radians
x_symbols = np.cos(x_radians) + 1j*np.sin(x_radians) # this produces our QPSK complex symbols
samples = np.repeat(x_symbols, 16) # 16 samples per symbol (rectangular pulses)
samples *= 2**14 # The PlutoSDR expects samples to be between -2^14 and +2^14, not -1 and +1 like some SDRs

# 启动发送端并发送信号
sdr.tx_cyclic_buffer = True # Enable cyclic buffers
sdr.tx(samples) # start transmitting

# 接收接收端的信号
for i in range (0, 10):
    raw_data = sdr.rx()  # Receive samples
rx_samples = sdr.rx()
print(rx_samples)

# 停止发送端
sdr.tx_destroy_buffer()

# 计算接收到的信号的功率谱密度
psd = np.abs(np.fft.fftshift(np.fft.fft(rx_samples)))**2
psd_dB = 10*np.log10(psd)
f = np.linspace(sample_rate/-2, sample_rate/2, len(psd))

# 绘制时域图
plt.figure(0)
plt.plot(np.real(rx_samples[::100]))
plt.plot(np.imag(rx_samples[::100]))
plt.xlabel("Time")

# 绘制频域图
plt.figure(1)
plt.plot(f/1e6, psd_dB)
plt.xlabel("Frequency [MHz]")
plt.ylabel("PSD")
plt.show()

以上代码生成了一个随机QPSK信号，通过ADI Pluto SDR设备将其传输，并使用Pluto SDR设备接收该信号。接收到的信号进行了功率谱密度分析，并绘制了频域图。

QPSK信号的功率谱密度图的特点是，其频谱表现为四个簇，每个簇对应QPSK信号的一个符号。每个簇的带宽约为基带信号的带宽，且由于使用矩形脉冲，每个簇的带宽之间有一定的重叠。此外，功率谱密度图中还可以看到一些其他频率分量，这些分量可能是由于接收信号中存在其他干扰或噪声导致的。

Namespace(weights='yolo7.pt', cfg='cfg/training/yolov7.yaml', data='data/DOTA_split.yaml', hyp='data/hyp.scratch.p5.yaml', epochs=10, batch_size=4, img_size=[640, 640], rect=False, resume=False, nosave=False, notest=False, noautoanchor=False, evolve=False, bucket='', cache_images=False, image_weights=False, device='', multi_scale=False, single_cls=False, ada m=False, sync_bn=False, local_rank=-1, workers=8, project='runs/train', entity=None, name='exp', exist_ok=False, quad=False, linear_lr=False, label_smoothing=0.0, upload_dataset=False, bbox_interval=-1, save_period=-1, artifact_alias='latest', freeze=[0], v5_metric=False, world_size=1, global_rank=-1, save_dir='runs\\train\\exp2', total_batch_size=4) tensorboard: Start with 'tensorboard --logdir runs/train', view at http://localhost:6006/ hyperparameters: lr0=0.01, lrf=0.1, momentum=0.937, weight_decay=0.0005, warmup_epochs=3.0, warmup_momentum=0.8, warmup_bias_lr=0.1, box=0.05, cls=0.3, cls_pw=1.0, obj=0.7, obj_pw= 1.0, iou_t=0.2, anchor_t=4.0, fl_gamma=0.0, hsv_h=0.015, hsv_s=0.7, hsv_v=0.4, degrees=0.0, translate=0.2, scale=0.9, shear=0.0, perspective=0.0, flipud=0.0, fliplr=0.5, mosaic=1.0, mixup=0.15, copy_paste=0.0, paste_in=0.15, loss_ota=1 Traceback (most recent call last): File "D:\Documents\Desktop\YOLO_suanfa\yolov7-main\train.py", line 618, in <module> train(hyp, opt, device, tb_writer) File "D:\Documents\Desktop\YOLO_suanfa\yolov7-main\train.py", line 64, in train data_dict = yaml.load(f, Loader=yaml.SafeLoader) # data dict File "D:\Documents\Desktop\YOLO_suanfa\yolov7-main\venv\lib\site-packages\yaml\__init__.py", line 79, in load loader = Loader(stream) File "D:\Documents\Desktop\YOLO_suanfa\yolov7-main\venv\lib\site-packages\yaml\loader.py", line 34, in __init__ Reader.__init__(self, stream) File "D:\Documents\Desktop\YOLO_suanfa\yolov7-main\venv\lib\site-packages\yaml\reader.py", line 85, in __init__ self.determine_encoding() File "D:\Documents\Desktop\YOLO_suanfa\yolov7-main\venv\lib\site-packages\yaml\reader.py", line 124, in determine_encoding self.update_raw() File "D:\Documents\Desktop\YOLO_suanfa\yolov7-main\venv\lib\site-packages\yaml\reader.py", line 178, in update_raw data = self.stream.read(size) UnicodeDecodeError: 'gbk' codec can't decode byte 0x80 in position 233: illegal multibyte sequence

这个错误是因为在读取 YAML 文件时使用了 GBK 编码，但在第233个位置出现了非法的多字节序列，导致无法解码。你可以尝试以下解决方法：

1. 将文件编码改为 UTF-8 或其他可支持的编码格式。
2. 使用适当的编码解码器来读取文件，例如使用 `utf-8` 编码器：

import codecs

with codecs.open('cfg/training/yolov7.yaml', 'r', encoding='utf-8') as f:
    data_dict = yaml.load(f, Loader=yaml.SafeLoader)

请确保你的代码中正确指定了文件的编码方式。