Update app.py

app.py

@@ -69,6 +69,7 @@ new_loss = scipy.stats.multivariate_normal(np.zeros(3), k_train_with_noise).logp
 new_loss_str = f"{new_loss:.4f}"
 
 def percentage_change():
+    global old_loss
     ans = (new_loss - old_loss)/old_loss * 100
     old_loss = new_loss
     return f"{ans:.1f}%"