Cleanup and move hinton_demo

Author: tonysyu

examples/api/hinton_demo.py

@@ -0,0 +1,41 @@
+"""
+Demo of a function to create Hinton diagrams.
+
+Hinton diagrams are useful for visualizing the values of a 2D array (e.g.
+a weight matrix): Positive and negative values are represented by white and
+black squares, respectively, and the size of each square represents the
+magnitude of each value.
+
+Initial idea from David Warde-Farley on the SciPy Cookbook
+"""
+import numpy as np
+import matplotlib.pyplot as plt
+
+
+def hinton(matrix, max_weight=None, ax=None):
+    """Draw Hinton diagram for visualizing a weight matrix."""
+    ax = ax if ax is not None else plt.gca()
+
+    if not max_weight:
+        max_weight = 2**np.ceil(np.log(np.abs(matrix).max())/np.log(2))
+
+    ax.patch.set_facecolor('gray')
+    ax.set_aspect('equal', 'box')
+    ax.xaxis.set_major_locator(plt.NullLocator())
+    ax.yaxis.set_major_locator(plt.NullLocator())
+
+    for (x,y),w in np.ndenumerate(matrix):
+        color = 'white' if w > 0 else 'black'
+        size = np.sqrt(np.abs(w))
+        rect = plt.Rectangle([x - size / 2, y - size / 2], size, size,
+                             facecolor=color, edgecolor=color)
+        ax.add_patch(rect)
+
+    ax.autoscale_view()
+    ax.invert_yaxis()
+
+
+if __name__ == '__main__':
+    hinton(np.random.rand(20, 20) - 0.5)
+    plt.show()
+