Making the numbers match topic numbers

ch-13/2.2-modelling-distances/graph_decay.py

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+from matplotlib import pyplot as plt
+import numpy as np
+
+m  = 250
+
+def decay_fn(x):
+    return 1.0 / (1 + (abs(x) / m) ** 2)
+
+x = np.arange(0, 1500)
+y = np.array([decay_fn(i) for i in x])
+plt.plot(x, y)
+
+# plot y=zero line in black
+plt.plot([0, 1500], (0, 0), color="black")
+
+# plot x=zero line in red
+plt.plot((0, 0), [0, 1], color="black")
+
+
+# plot the standard deviation of the decay function
+# std_dev = np.std(x)
+# print(std_dev)
+# plt.plot((std_dev, std_dev), [0, 1], color="yellow", linestyle="--")
+
+# plot m line in dashed blue
+plt.plot((m, m), [0, 1], color="red", linestyle="--")
+
+
+plt.show()