FIX does not draw the ellipse! scikit-learn#6640 (scikit-learn#6757)

* FIX does not draw the ellipse! scikit-learn#6640

* Give ellipses a higher z-order, yellow border, and thicker border.

* Add an alpha level to the markers so that it is easier to tell how
many there are.

* Change false positive to asterisks so that they have similar sizes as
the true positives.

* Fix line too long issue

Author: saiwing-yeung

examples/classification/plot_lda_qda.py

@@ -68,13 +68,19 @@ def plot_data(lda, X, y, y_pred, fig_index):
     X0_tp, X0_fp = X0[tp0], X0[~tp0]
     X1_tp, X1_fp = X1[tp1], X1[~tp1]
 
+    alpha = 0.5
+
     # class 0: dots
-    plt.plot(X0_tp[:, 0], X0_tp[:, 1], 'o', color='red')
-    plt.plot(X0_fp[:, 0], X0_fp[:, 1], '.', color='#990000')  # dark red
+    plt.plot(X0_tp[:, 0], X0_tp[:, 1], 'o', alpha=alpha,
+             color='red')
+    plt.plot(X0_fp[:, 0], X0_fp[:, 1], '*', alpha=alpha,
+             color='#990000')  # dark red
 
     # class 1: dots
-    plt.plot(X1_tp[:, 0], X1_tp[:, 1], 'o', color='blue')
-    plt.plot(X1_fp[:, 0], X1_fp[:, 1], '.', color='#000099')  # dark blue
+    plt.plot(X1_tp[:, 0], X1_tp[:, 1], 'o', alpha=alpha,
+             color='blue')
+    plt.plot(X1_fp[:, 0], X1_fp[:, 1], '*', alpha=alpha,
+             color='#000099')  # dark blue
 
     # class 0 and 1 : areas
     nx, ny = 200, 100
@@ -104,7 +110,8 @@ def plot_ellipse(splot, mean, cov, color):
     angle = 180 * angle / np.pi  # convert to degrees
     # filled Gaussian at 2 standard deviation
     ell = mpl.patches.Ellipse(mean, 2 * v[0] ** 0.5, 2 * v[1] ** 0.5,
-                              180 + angle, color=color)
+                              180 + angle, facecolor=color, edgecolor='yellow',
+                              linewidth=2, zorder=2)
     ell.set_clip_box(splot.bbox)
     ell.set_alpha(0.5)
     splot.add_artist(ell)