Update 4_sommerfeld_model.md

src/4_sommerfeld_model.md

@@ -133,7 +133,7 @@ Estates = kstates**2;
 
 fig = pyplot.figure();
 ax = fig.add_subplot(111);
-ax.fill_between(kfilled, Efilled, kf*kf);
+ax.fill_between(kfilled, Efilled, kf*kf, alpha=0.5);
 ax.plot([kf, kf], [0.0, kf*kf], 'k:');
 ax.plot(kstates, Estates, 'k--');
 ax.plot(kfilled, Efilled, linewidth=4);