add ch1.py

Author: coolfish-a

ch1.py

@@ -0,0 +1,12 @@
+from matplotlib import pyplot as plt
+#%matplotlib inline
+variance = [1,2,4,8,16,32,64,128,256]
+bias_squared=[256,128,64,32,16,8,4,2,1]
+total_error=[x+y for x,y in zip(variance,bias_squared)]
+xs = [i for i,_ in enumerate(variance)]
+plt.plot(xs,variance,'g-',label='variance')
+plt.plot(xs,bias_squared,'r-',label='bias^2')
+plt.plot(xs,total_error,'b:',label='total_error')
+plt.title('bias variance')
+plt.legend(loc=9)
+plt.show()