Merge pull request #255 from Nin17/master

correct 2D Gaussian + add separable alternative answer

Author: rougier

source/exercises100.ktx

@@ -719,10 +719,18 @@ Generate a generic 2D Gaussian-like array (★★☆)
 hint: np.meshgrid, np.exp
 
 < a56
-X, Y = np.meshgrid(np.linspace(-1,1,10), np.linspace(-1,1,10))
-D = np.sqrt(X*X+Y*Y)
+X, Y = np.meshgrid(np.linspace(-1, 1, 10), np.linspace(-1, 1, 10))
 sigma, mu = 1.0, 0.0
-G = np.exp(-( (D-mu)**2 / ( 2.0 * sigma**2 ) ) )
+G = np.exp(-((X - mu) ** 2 + (Y - mu) ** 2) / (2.0 * sigma**2))
+print(G)
+
+# Another solution using the fact that a 2D Gaussian is separable
+# Author: Nin17
+x = np.linspace(-1, 1, 10)
+y = np.linspace(-1, 1, 10)
+gx = np.exp(-((x - mu) ** 2 / (2.0 * sigma**2)))
+gy = np.exp(-((y - mu) ** 2 / (2.0 * sigma**2)))
+G = gy[:, None] * gx[None, :]
 print(G)
 
 < q57