routine

plt/logistic.py

@@ -0,0 +1,40 @@
+import numpy as np
+import matplotlib.pyplot as plt
+
+def logistic_function(x, w, b):
+    return 1 / (1 + np.exp(-(w * x + b)))
+
+def cost_function(f_wb, y):
+    if y == 1:
+        return -np.log(f_wb)
+    else:
+        return -np.log(1 - f_wb)
+
+f_wb = np.linspace(-1, 2, 100)  # 避免log(0)的情况
+
+cost_y1 = cost_function(f_wb, 1)
+cost_y0 = cost_function(f_wb, 0)
+
+plt.figure(figsize=(12, 6),dpi=600)
+
+plt.subplot(1, 2, 1)
+plt.plot(f_wb, cost_y1, label='y=1')
+plt.title('Cost Function when y=1')
+plt.xlabel('f_wb')
+plt.ylabel('Cost')
+plt.axhline(0, color='black', linewidth=0.8)  # 增加水平坐标轴
+plt.axvline(0, color='black', linewidth=0.8)  # 增加垂直坐标轴
+plt.legend()
+
+plt.subplot(1, 2, 2)
+plt.plot(f_wb, cost_y0, label='y=0')
+plt.title('Cost Function when y=0')
+plt.xlabel('f_wb')
+plt.ylabel('Cost')
+plt.axhline(0, color='black', linewidth=0.8)  # 增加水平坐标轴
+plt.axvline(0, color='black', linewidth=0.8)  # 增加垂直坐标轴
+plt.legend()
+
+plt.tight_layout()
+#plt.show()
+plt.savefig('plt/logistic_cost_function.png')